Unit 5 Radicals and Equations of a Line
•This unit has a review section on solving/reducing
radicals, and the laws of exponents.
•This is required to solve the Pythagorean Theorem.
•This unit also covers the three standard equation of a
line used to graph in the coordinate plane (Standard
equation, slope-intercept, and point-slope).
•The distance formula, midpoint, endpoint, and slope
are all addressed in the coordinate plane, as well as
parallel and perpendicular lines.
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Standards
SPI’s taught in Unit 5:
SPI 3108.1.4 Use definitions, basic postulates, and theorems about points, lines, angles, and planes to write/complete proofs and/or to solve
problems.
SPI 3108.3.1 Use algebra and coordinate geometry to analyze and solve problems about geometric figures (including circles).
SPI 3108.3.2 Use coordinate geometry to prove characteristics of polygonal figures.
CLE (Course Level Expectations) found in Unit 5:
CLE 3108.1.4 Move flexibly between multiple representations (contextual, physical written, verbal, iconic/pictorial, graphical, tabular, and symbolic),
to solve problems, to model mathematical ideas, and to communicate solution strategies.
CLE 3108.1.7 Use technologies appropriately to develop understanding of abstract mathematical ideas, to facilitate problem solving, and to produce
accurate and reliable models.
CLE3108.2.3 Establish an ability to estimate, select appropriate units, evaluate accuracy of calculations and approximate error in measurement in
geometric settings.
CLE 3108.3.1 Use analytic geometry tools to explore geometric problems involving parallel and perpendicular lines, circles, and special points of
polygons.
CFU (Checks for Understanding) applied to Unit 5:
3108.1.1 Check solutions after making reasonable estimates in appropriate units of quantities encountered in contextual situations.
3108.1.2 Determine position using spatial sense with two and three-dimensional coordinate systems.
3108.1.3 Comprehend the concept of length on the number line.
3108.1.5 Use technology, hands-on activities, and manipulatives to develop the language and the concepts of geometry, including specialized
vocabulary (e.g. graphing calculators, interactive geometry software such as Geometer’s Sketchpad and Cabri, algebra tiles, pattern blocks,
tessellation tiles, MIRAs, mirrors, spinners, geoboards, conic section models, volume demonstration kits, Polydrons, measurement tools,
compasses, PentaBlocks, pentominoes, cubes, tangrams).
3108.1.7 Recognize the capabilities and the limitations of calculators and computers in solving problems.
3108.2.6 Analyze precision, accuracy, and approximate error in measurement situations.
3108.3.1 Prove two lines are parallel, perpendicular, or oblique using coordinate geometry.
3108.3.2 Connect coordinate geometry to geometric figures in the plane (e.g. midpoints, distance formula, slope, and polygons).
3108.3.4 Apply the midpoint and distance formulas to points and segments to find midpoints, distances, and missing information in two and three
dimensions.
3108.4.3 Solve problems involving betweeness of points and distance between points (including segment addition).
3108.4.19 Use coordinate geometry to prove properties of plane figures.
Reducing a Radical
There are three conditions that must be met for
a radical expression to be in its simplest
form:
1. The number under the radical sign has no
perfect square factors other than 1
2. The number under the radical sign does not
contain a fraction
3. A denominator does not contain a radical
expression
Reducing the Square Root of
a Fraction
Reduce this Square Root: √4/3
• We can rewrite this = √4 /√3
• The square root of 4 is 2, so we now have:
2/√3.
• We cannot stop here, there is a radical in the
denominator.
• Therefore, we multiply the top and bottom by
top and bottom by √3/√3 ( a form of 1)
• So…( 2* √3) / ( √3* √3) = 2 √3 / 3
Reducing a Radical with a
Perfect Square
• Reduce this radical: √24/ √3
• The square root of 24 can be rewritten as: (√4*
√6)/ √3
• We can solve the square root of four (it is 2) and
now have: (2* √6)/ √3
• The square root of 6 can be rewritten as the
square root of 2 times the square root of 3, which
gives us: ( 2* √2* √3)/ √3
• We can cancel out the square roots of 3, and now
we have: 2* √2
A Deeper Look at Reducing
Radicals
• Ultimately, to reduce radicals we look for
perfect squares
• For example, reduce this: √75
• This has one perfect square in it: 25
• Therefore, we have 25*3, which is 5*5*3
• Therefore we can reduce this to: 5 √3
• There are three ways to reduce a
radical:
How to Reduce a Radical
1. Recognize perfect squares. If you
know your perfect squares up to about
13, you can often reduce a radical in
your head (like reducing √75)
2. The Factor Tree. Whee 
3. Using a Calculator
• What A calculator? How????
Recognize the Square
• Reduce this: √60
– This is 4 x 15. Therefore it reduces to 2 √15
• Reduce this: √45
– This is 9 x 5. Therefore it reduces to 3 √5
• Reduce this: √90
– This is 9 x 10. Therefore it reduces to 3 √10
• This is a good method for simple radicals
Factor Tree
• Reduce this: √80
– The factor tree requires you to reduce a
number to it’s prime numbers
– 80 is 8 x 10, which is 2 x 2 x 2 x 2 x 5
– Therefore, I can pull out the 2’s and leave
the five
– This gives me 4 √5
• Most of you remember how to do this
Calculator
• Let’s look at this one again: √80
• Again, I’ll look for perfect squares, but
this time using the calculator
• Go to the “y=“ button (top left)
• Enter this: 80/x2 (use the “x,t,Ø,n” button
for X, and then use the “squared button”)
• This forces the calculator to divide 80 by
every single rational number from 1 to 80
Calculating the Square
• The calculator first assigns X the value
of 1. Therefore Y is 80 (80/12)
• It then continues up in infinite
increments basically forever
• What we want to do is identify the
largest value of X, and whatever is left
over will still be under the radical sign
The Table
• After we enter 80/x2, we need to enter this:
• Press the “2nd” button, then “table F5” (top
right button)
• Here you will see an X / Y chart
• What we focus on is the “Y” column
• We need to find the smallest value of Y,
where Y is a whole number greater than 1 (1
can’t be a perfect square, right?)
Analyzing the Table
• As we look at the table, we see that the
smallest whole number in the Y table is 5
• We see the X value is 4
• We can therefore write this: 4 √5
• Remember, the value of Y is what is left
under the radical sign
• If we cannot find a whole number for Y, we
cannot reduce the fraction
Try Another
• Reduce this using the Calculator: √135
• Go to the “y =“ button (you may have to hit “clear”
to remove your last problem) and enter: 135/X2
• Now hit “2nd” and “Table”
• We look for the smallest whole value of Y, and find
15. The matching X value is 3
• So we write: 3 √15
• To confirm this is right, we would multiply 3 x 3 x
15, and we get 135.
Example
• You try:
• √175
 Answer: 5 √7
• √294
 Answer: 7 √6
• √168
 Answer: 2 √42
• √270
 Answer: 3 √30
Assignment
• Page 399 1-15
• 3 Radicals Worksheets
Unit 5 Quiz 1
Reduce all radicals to their simplest form
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
√156
√240
√340
√76
√40
√150
√196
√90
√220
√540
Answers
1. 2 √39
2. 4 √15
3. 2 √85
4. 2 √19
5. 2 √10
6. 5 √6
7. 14
8. 3 √10
9. 2 √55
10. 6 √15
Unit 5 Quiz 2
Reduce all radicals to their simplest form
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
(√156) – (√72)
(√240) + (√15)
(√340) / 2
(√76) / (√19)
(√40) * (√20)
(√150) – (√24)
(√196) – (√36)
(√90) / 6
√(240/10)
(√540) + (4√15)
Answers
1. 2√39 - 6√2
2. 5√15
3. √85
4. 2
5. 20√2
6. 3√6
7. 8
8. (√10) / 2
9. 2√6
10. 10√15
Multiplying with Exponents
• A quick look at exponents
• When multiplying the same base
number with exponents, add the
exponent
• For example: 53 x 52 = 55
• This is the same as writing this:
• 51 x 51 x 51 x 51 x 51 which equals 55
53
52
Multiplying with Exponents
• What is y3 x y3
– it would be y6
• What is ya x yb
– it would be ya+b
• What is m6 x m-4
– it would be m2
• What is n2 x n3 x n
– it would be n6
Parenthesis and Exponents
• When we have parenthesis, we multiply the
outer exponent times the inner exponent
• For example (x4)3 = x12
• This is because we are really doing this:
• (x4) x (x4) x (x4)
• And we know that when multiplying the same
base number, we add exponents
• Thus we add the exponents 4 + 4 + 4 = 12
• Which is how we get x12
Parenthesis and Exponents
• What is (x5)3
– It would be x15
• What is (5x2)2
– It would be 52x4
• What is (52x3)-2
– It would be 5-4x-6
• What is (3-3y-4)-2
– It would be 36y8
Dividing with Exponents
• Dividing base numbers with exponents
• When we divide the same base number with
exponents, we take the top exponent minus
the bottom exponent
• For example:
• X5/X3 = X2
• An example with real numbers: 53/52 = 5
• This is 125/25 = 5, so we have proved this to
be true
Dividing with Exponents
• What is 105/102
– It would be 103
• What is x7/x3
– It would be x4
• What is 53x5/5x2
– It would be 52x3
• What is 43y2/45y7
– It would be 4-2y-5
Creating Positive Exponents
• Negative exponents are not considered
“simplified”
• A proper answer in math will only have
positive exponents
• To turn a negative exponent into a positive
exponent, put it under a dividing line
• For example: 10-2 = 1/102
• This can be rewritten as 1/100
• Here is how it works…
There is a Pattern
•
•
•
•
•
•
•
•
103 = 1000
102 = 100
101 = 10
100 = 1
10-1 = 1/101
10-2 = 1/102 or 1/100
10-3 = 1/103 or 1/1000
So we simply put the base number under the divider
line and turn the negative exponent into a positive
exponent
Converting Negative Exponents
• What if the exponent is already under the
dividing bar, and is negative?
• For example: 5/x-2
• In this case, we move the number above the
dividing bar and make it positive: 5x2
• So our rule will be this: If we have a negative
exponent, go to the opposite side of the
dividing bar, and rewrite the exponent as a
positive exponent
Converting Negative Exponents
• What is x-3
– It would be 1/x3
• What is 5-2y-6
– It would be 1/52y6
• What is 4-3y4/x2z-3
– It would be y4z3/43x2 –Here we moved the 43 under
the dividing line, and the z3 above the dividing line,
and left the other two variables where they were
• What is 4-3/4-5
– It would be 45/43, or 45-3 or 42
The Zero Exponent
• ANYTHING TO THE ZERO POWER IS
ONE.
• 1
• ONE
• 1!
• Get it?!!!
• For example 50 = 1, or x0 = 1
Solving the Zero Exponent
• What is 5a0
– It would be 5 (because 5 x 1 = 5)
• What is 5ab0
– It would be 5a (because 5 x a x 1 = 5a)
• What is (45810x9y2)0
– It would be 1 (that whole expression is to the zero
power, so the whole thing is 1)
• What is (2343y8)0 x (1210y8z9)0
– It would be 1 x 1, which is of course 1.
Summary
• Multiplying base numbers: Add exponent
• Dividing base numbers: Subtract bottom
exponent from top exponent
• Exponents in Parenthesis: Multiply outside
exponent times inside exponent
• Negative Exponents: Move expression to
opposite side of dividing line, convert
exponent from negative to positive
• Exponent = 0, the entire expression which is
raised to the zero power = 1
Unit 5 Quiz 2a
Reduce all radicals to their simplest form
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
(√156) – (√72)
(√240) + (√15)
(√340) / 2
(√76) / (√19)
(√40) * (√20)
(√150) – (√24)
(√196) – (√36)
(√90) / 6
√(240/10)
(√540) + (4√15)
Answers
1. 2√39 - 6√2
2. 5√15
3. √85
4. 2
5. 20√2
6. 3√6
7. 8
8. (√10) / 2
9. 2√6
10. 10√15
Unit 5 Quiz 3
1.
When multiplying numbers with the same base, you ________
exponents
2. When dividing numbers with the same base, you _______ the
bottom exponent from the top exponent
3. When solving exponents in parenthesis, you ________ the
outer exponent times the inner exponent
4. When solving negative exponents, you _______ the base
number, and make the exponent positive
5. Any number with an exponent of zero = __________
6. Reduce (leave in exponent form): m6 x m-4 = ________
7. Reduce (leave in exponent form): (5x2)2 = ____________
8. Reduce (leave in exponent form): x7/x3 = _____________
9. Reduce (leave in exponent form): 5-2y-6 = _____________
10. Reduce: (2343y8)0 x (1210y8z9)0 = _________________
Reducing Radicals with
Exponents
Example
1. √13
2. √13 x √13
3. (√13)2
4. √a
5. (√a)2
6. √a2
7. √a3 = √ a2 x a
8. √a4 = √ a2 x a2
9. √a5 = √ a4 x a
10. √a6 = √ a3 x a3
Answer
1. √13
2. 13
3. 13
4. √a
5. a
6. a
7. a √a
8. a2
9. a2 √a
10. a3
Assignment
• Page 829 1-20
• Exponents Handout
• Another Exponents Handout
Pythagorean Theorem (500 BC)
• It was believed that Pythagoras discovered this
theorem when waiting for the tyrannical ruler,
Polycrates.
• While looking at the floor’s square tiling of the palace
of Polycrates, Pythagoras thought of this interesting
idea: A diagonal line may be used to cut or divide the
square, and two right triangles would be produced
from the cut sides.
• Other stories tell us that he then spent time on the
sand at a beach drawing diagrams until he came up
with the final equation
The Distance Formula
• Background: The distance formula is
based upon the Pythagorean Theorem
• The Pythagorean Theorem states that
in a right triangle, where you have side
A, side B, and side C, you can calculate
a side thusly: a2 + b2 = c2, where c is the
hypotenuse, or the longest side of the
right triangle
Distance Formula
• You can draw any
line on a graph,
and then create a
right triangle with
that line as the
hypotenuse
And
So
On
Distance Formula
• Remember, to find the length
of the hypotenuse (the long
side C) we need to know the
length of the two short sides
(side A and side B)
• We can easily calculate that –
it would be the big number
minus the small number –just
like on a ruler
• So the length of side A is the
big x number minus the small
x number = 4 – (-4) = 8
• The length of side B is the big
Y number minus the small Y
number = 5 – (-2) = 7
(4,5)
C
(-4,-2)
B
A
(4,-2)
Distance Formula
• From the previous slide,
we know that side A is 8
units long, and side B is
7 units long
• We also know that A2 +
C
2
2
B =C
• So we have 82 + 72 = C2
• Therefore to find out how
(-4,-2)
long C is, we have to
take the square root of
both sides:
• √C2 = √(82 + 72)
• Or: C = √(82 + 72)
So C = 10.63
(4,5)
B
A
(4,-2)
Distance Formula
-I will ask this equation on a test
• Using the previous example, we can come
up with a formula which will work to find
the distance of any line:
• Instead of C =, we will D = (for distance)
• d= √(x2-x1)2 + (y2-y1)2
• Remember, this is big x minus small x, and
then square it, and big y minus small y,
and then square it, add those two squares,
then take the square root of that sum
Examples
• Given point a (5,2) and point b (-4,-1)
find the distance between the two points
• D = √(5-(-4))2 + (2 – (-1))2
• D = √(9)2 + (3)2
Would it matter if you
subtracted the numbers the
• D = √(81 + 9)
other way around? Hmm…
2 + (-1 -2)2
D
=
√(-4
–
5)
• D = √90
D = √(-9)2 + (-3)2
D = √(81 + 9
• D = 9.48
D = √(90)
D = 9.48
no, it does not
matter
Midpoint
• If you wanted to know the halfway point
between two numbers, you would add
them together, and divide by two.
• For example, what is halfway between 1
and 9?
• 1 + 9 = 10, then divide by 2, or 10/2 = 5
• Therefore, 5 is the midpoint of 1 and 9
Midpoint Formula
• If we have segment AB, with the
coordinates of A = (x1, y1) and the
coordinates of B = (x2, y2) all we do is
add the “x”s and divide by two, and add
the “y”s and divide by two.
• We will call the midpoint M.
• Therefore, to find Mx = {[(x1+ x2)/2],
My = {[(y1+ y2)/2]}
Example
• Segment QS has endpoints Q (3,5) and
S (7,-9)
• What is the midpoint M?
• X coordinate of M = (3+7)/2 = 5
• Y coordinate of M = (5 + -9)/2 = -2
• The coordinates for midpoint M = (5,-2)
• By the way. I have this loaded on my
calculator. You’re welcome to have it. 
Finding an Endpoint
• What if you have an endpoint, and a midpoint, and
want the other endpoint?
• The midpoint of Segment AB = (3,4)
• Endpoint A = (-3,-2)
• What is Endpoint B?
• Just substitute into the midpoint formula
• Solving for X2, we have 3 = (-3 +X2)/2
– Therefore, -3 + X2 = 6, and X2 = 9
• Solving for Y2, we have 4 = (-2 + Y2)/2
– Therefore, -2 + Y2 = 8, and Y2 = 10
• The coordinates for B = (9,10)
Assignment
• Page 54 6-44
• Worksheet 1-6
• Pythagorean Theorem Word Problems
Handout
• Pythagorean Word Problems #2
Unit 5 Quiz 4
1.
2.
3.
Problems 1 through 5: Graph
points A,B,C,D,E (Hand draw
one graph with five points –
label each)
Problems 6 through 10: Use
the same points: Calculate
the midpoint between the two
points in each set – show
answers below graph
Problems 11 through 15:
Use the same points:
Calculate the distance
between the two points in each
set – show answers below
graph
#6, #11. A (1,4) B (3,-5)
#6 (midpoint) #11 (distance)
#7, #12. C (0,1) D (2, 6)
#7 (midpoint) #12 (distance)
#8, #13. E (0,0) F (4,6)
#8 (midpoint) #13 (distance)
#9, #14. G (-3,-4) H (-2,7)
#9 (midpoint) #14 (distance)
#10, #15. J (-1,6) K (4,9)
#10 (midpoint) #15 (distance)
Quiz Graph Answers
Midpoint:
6. :__________
7. :__________
8. :__________
9. :__________
10. :__________
.
..
.
Distance:
11. :__________
12. :__________
13. :__________
14. :__________
15. :__________
D
A
C
E
.
B
Slope
• Slope
• The slope of a line is a measure of how “tilted” the line is. A
highway sign might say something like “6% grade ahead.” What
does this mean, other than that you hope your brakes work?
What it means is that the ratio of your drop in altitude to your
horizontal distance is 6%, or 6/100. In other words, if you move
100 feet forward, you will drop 6 feet; if you move 200 feet
forward, you will drop 12 feet, and so on.
Slope
• In Geometry, we don’t measure percent (usually)
• We measure the rate of change
• We write this as a ratio, with amount of “Y” change on
top, and “X” change on bottom
• Here, the Y coordinate changed “+2” and the X
coordinate changed “+4” so the slope is 2/4, or 1/2
Slope
• The next question is, how do we measure the rate of
change?
• *We usually use m to indicate slope, and m =
rise/run, or (Y2-Y1) / (X2-X1)
• Looking at our previous picture, we see how we got 2
steps, and 4 steps:
We take
(4-2)/(5-1)
Or 2/4
Or 1/2
Slope Intercept Form
• There are three basic equations of a line (also known
as linear equations):
• *The first is Slope Intercept Form:
• *y = mx + b
•
*m = the slope of the line, and b = the y intercept. In
other words, if x = 0, then where does Y “intercept the
x axis” – thus “Y intercept”
• NOTE: Here you are only given the slope, but can
easily calculate a point (the Y intercept)
Slope Intercept Form
• Y = mX+b
• You MUST KNOW what m is, and what b is.
• When I ask you on the test “What is the slope
of the line?” You need to know to look at the
number in front of x.
• When I ask you “What is the Y intercept?”
Then you need to know to look at b.
• Or, if I ask you “If x is zero, what is y?” You
need to know to look at the intercept.
Example of Slope Intercept Form
• Graph the line y = ¾ X + 2
• ALWAYS ASK YOURSELF
THIS QUESTION:
• IF X IS ZERO, WHAT IS Y?
• Here, if X is 0, Y is 2
• So our first point is (0,2)
• Using slope, we just go up 3
and over 4 (from our first
point)
• So our second point is (4,5)
• By the way, your calculator
is already programmed to do
this. Just go to the “Y =“
button
.
.
Standard Form (of a Linear Equation)
• *The second linear equation is “the Standard
Form”
• *The standard form of a Linear Equation is
Ax + By = C
• *The easiest way to graph using this form is
to find the Y Intercept, and the X intercept
• *In other words, “IF X IS ZERO WHAT IS
Y,” AND “IF Y IS ZERO WHAT IS X” this
will give you two easy points to plot
• NOTE: Here, you are not given a point or a
slope
Example of Standard Form
• Graph 6x + 3y = 12
• Solve for X = 0.
• 3y = 12
• Y=4
• So one point is (0,4)
• Solve for Y = 0.
• 6x = 12
• X=2
• So one point is (2,0)
• Graph the 2 points, and
connect the dots.
.
.
Example of Standard Form
•
•
•
•
•
•
•
Graph -2x + 4y = -8
If x is 0
4Y = -8
Y = -2, Point: (0,-2)
If y is 0
-2x = -8
X = 4, Point: (4,0)
.
.
Point Slope Form
• *The 3rd equation of a line is Point Slope
Form
• y- y1 = m(x – x1)
• NOTE: Here you are given a point and
the slope
Example Point Slope Form
• Write an equation of a line with point (-1,4) and slope
3
• Notice, they don’t state which equation to use, but
they give you a point and the slope, so you use
point/slope
• y-4 = 3(x – (-1))
• y-4 = 3x + 3
• NOTE: This is simplified far enough, unless you need
to graph it. If so, you would simplify one step more:
• y = 3x + 7 – you could use a calculator now
Given 2 Points
• What if you are asked to write an equation of
a line given 2 points?
• A (-2,3) and B(1,-1)
• 1st, find the slope (y2-y1)/(x2-x1)
• m = (-1-3)/(1-(-2)) = -4/3
• Now use Point Slope Form:
• y- y1 = m(x – x1)
• y-(3) = -4/3(x-(-2)) and simplify
• y-3 = -4/3(x + 2)
Unit 5 Bellringer 1 (10 points)
Draw a picture, write the equation!
• Tom wants to fly a kite higher than Jerry.
• Jerry can fly his kite 50 feet high.
• Tom stands 35 feet away from a point
directly below his kite.
• If Tom has a kite string that is 65 feet
long, how high is his kite?
• Is Tom’s kite higher than Jerry’s?
Equations for Horizontal Lines
• Write an equation for a
horizontal line through
the point (3,2)
• Notice all points on the
(3,2)
line have the same Y
value. That is, Y = 2 no
matter what. So a
horizontal line through
the point (3,2) would be
• Y = 2 (it doesn’t matter Rule: An equation for a
horizontal line is Y = the
what X is)
.
given value of Y
Slope of Horizontal Line
• What is the slope of
this line?
• Slope =
• (y1-y2) / (x1-x2)
• =(2 – 2)/ (-3 – 3)
• = 0/-6
• =0
• Slope of a horizontal
line is ZERO!!!
.
(-3,2)
.
(3,2)
Equations for Vertical Lines
• Write an equation for a
vertical line through the
point (3,2)
• Notice all points on the
(3,2)
line have the same X
value. That is, X = 3 no
matter what. So a
vertical line through the
point (3,2) would be
• x = 3 (It doesn’t matter Rule: An equation for a
vertical line is X = the
what Y is)
.
given value of X
Slope of Vertical Line
• What is the slope of
this line?
• Slope =
• (y1-y2) / (x1-x2)
• =(2 – - 2)/ (3 – 3)
• = 4/0
• = UNDEFINED
• Slope of a Vertical
line is UNDEFINED!!!
.
.
(3,2)
(3,-2)
Assignment
• Page 194 8-19, 24-37
• Worksheet 3-5
Unit 5 Quiz 5
Write the equation for a line in “Slope Intercept” form
Write the equation for a line in “Standard Form”
Write the equation for a line in “Point Slope” form
Which equation would you use to graph a line if you were given the Y
intercept and the slope? (write the name not the equation)
5. Which equation would you use if you were given one point and the
slope? (write the name, not the equation)
6. Which equation is easiest to graph if you solve for the X and Y
intercepts (if x is zero what is y, and if y is zero what is x)? (name)
7. Using this point: (3,2) write an equation for a line that is horizontal,
and goes through this point
8. Using this point: (3,2) write an equation for a line that is vertical, and
goes through this point
9. What is the slope of this line: Y = 1/2X + 5
10. Graph this line on your calculator, and leave it on so I may check it:
Y = 2/3X - 4
1.
2.
3.
4.
Answers
1. .
2. .
3. .
4. .
5. .
6..
7..
8..
9..
10..
Parallel Lines
• Previously, we learned that if 2 lines are parallel, then they
do not intersect, and they are co-planar. Assuming they
are co-planar, how do we know that they do not
intersect?
• If two lines are parallel, then they have equal slopes –
this means they won’t intersect
• If two lines have equal slopes, then they are parallel
• By definition: Any two (or more) vertical lines are parallel
– why do we have to say by definition?
• By definition: Any two (or more) horizontal lines are
parallel
– why do we have to say by definition?
Checking for Parallel
• How do you check to see if two lines are
parallel?
• Compare their slopes. If they are
equal, then they are parallel
• Are lines 4y= 12x + 20, and y = 3x -1
parallel?
Comparing Lines/Slopes
•
•
•
•
•
•
Rewrite 4y = 12x + 20 in slope intercept form
4y = 12x + 20  Divide by 4
y = 3x + 5
The other equation was y = 3x – 1
Compare slopes
They have the same slope (it is 3), therefore they
are parallel
• Also notice that they have different y intercepts
(5, and -1). If they had the same intercept, they
would be the same line
Another Example
• Are these lines
parallel?
• Compare slopes
• Line a slope =
• (4-(-2))/(-2-(-5)) = 2
• Line b slope =
• (5-(-2))/(4-2) = 3 1/2
• The slopes are not
equal, the lines are not
parallel
.
(-2,4)
.
(4,5)
a
.
(-5,-2)
b
.
(2,-2)
You CANNOT compare by
just “eyeballing it” –you
MUST compare slopes
Writing Equations of Parallel
Lines
• Given: a line with this equation: y = - 4x + 3
• Given: a point at (1,-2)
• Write an equation of a line parallel to the first
line, going through the given point
• Just write a point slope equation using the
slope of the first line, and the given point:
• y-y1 = m(x-x1) or y-(-2) = - 4(x-1)
• Which simplifies to y + 2 = -4(x – 1)
Slopes of Perpendicular Lines
• What is the slope of this
line?
• The slope is 1(up one
over one) or 1/1
• Draw a perpendicular
line
• (remember
perpendicular means 90
degree angle)
• What is the slope of the
new line?
• The slope is -1 (down
one over one) or -1/1
.
.
.
.
.
.
..
..
..
Compare Slopes
a
b
•
•
•
•
What is the slope of Line a? Of line b?
Line a: Slope = 1/2. Line b: Slope = -2
What is the slope of line c? Of line d?
Line c: Slope = 3. Line d: Slope = -1/3
c
d
Conclusions
• What can you conclude about the slopes of the
perpendicular lines in the previous examples?
• If you multiply the slopes together, you always
get -1. In other words: “The product of the slopes
is -1.” KNOW THIS!!
• We call this idea “negative reciprocals”
• 3 x -1/3 = -1 or 3/1 x -1/3 = -1
• ½ x -2 = -1 or ½ x -2/1 = -1
• 1 x -1 = -1 or 1/1 x -1/1 = -1
• In each case, the negative “opposite” is the slope of
the second line
Remember this: “Flip it, and use the opposite sign”
Summary of Perpendicular
Lines
• If 2 lines are perpendicular, the product
of their slopes is -1
• If the slope of 2 lines have a product of
-1, then the lines are perpendicular
• By Definition: Any horizontal line and
vertical line are perpendicular
– Why by definition?
Example
• Write an equation for the line
perpendicular to the line y = -3x -5 that
goes through the point (-3,7)
• Simply use the point slope form
• Identify the negative reciprocal of the
slope of the first line. The first slope was
–3, so the negative reciprocal is 1/3
• y-7 = 1/3(x-(-3)) or y-7 = 1/3(x+3)
Example
• Write an equation of the line
perpendicular to 5y – x = 10 that
contains the point (15,-4)
• Solve the first equation for y:
• 5y = x + 10
• y = 1/5 x + 2
• Negative reciprocal: -5. Therefore:
• y-(-4) = -5(x-15) or y+4 = -5(x-15)
Example
• Write an equation of a line
perpendicular to y = 2/3x
• Here, we aren’t given any points, or an
intercept, so we can use any
perpendicular line, not one which goes
through a specific point. All we need is
the negative reciprocal
• y = -3/2x
Assignment
• Text: Page 201-202 7-21
• Worksheet 3-6
Unit 5 Quiz 6
• Write the equations for:
1. Distance Formula
2. Point Slope Equation
3. Pythagorean Theorem
4. Midpoint Equation
5. Standard Form Equation
6. Slope Intercept Equation
7. Slope Equation
8. How do you know two lines are parallel on a graph?
9. How do you know two lines are perpendicular on a
graph?
10. True/False The product of the slopes of parallel lines
is -1
Unit 5 Quiz 7
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
What is the first rule of solving radicals?
What is the second rule of solving radicals?
What is the third rule of solving radicals?
What is the first rule of solving exponents?
What is the second rule of solving exponents?
What is the third rule of solving exponents?
What is the fourth rule of solving exponents?
What is the rule of the zero exponent?
Give an example of an equation for a horizontal line
Give an example of an equation for a vertical line
Unit 5 Final Extra Credit (6 points)
• Little Timmy wants to fly his kite higher than anybody
• Little Timmy is standing 140 feet away from a point
on the ground directly under his kite (the point is
under his kite)
• Little Timmy’s kite string is 260 feet long
• Little Janie has her kite 220 feet high in the air
1. How high is little Timmy’s Kite? (2 pts) –Show
equation
2. Who is higher, little Timmy or little Janie? (1 pt)
3. Draw a picture showing little Timmy and his kite.
Label all 3 sides of the triangle (3 pts)