How do you find b?
How do you find b?
How do you find b?
“DRY”
How do you find b (dry)?
Review
What is slope-intercept form?
Y = mX + b
?
Review
What is slope-intercept form?
Y = mX + b
Input
Review
What is slope-intercept form?
Y = mX + b
?
Review
What is slope-intercept form?
Y = mX + b
Output
Review
What is slope-intercept form?
Y = mX + b
?
Review
What is slope-intercept form?
Y = mX + b
Rate of change
a.k.a. Slope
Review
What is slope-intercept form?
Y = mX + b
?
Review
How do you find b?
What is slope-intercept form?
Y = mX + b
Starting amount
a.k.a. ‘y-intercept’
Riddle
b
I started with some money.
m
Every week I earned $100.
After 4 weeks, I had $900.
How much did I start with?
X
Y
Riddle
b
I started with some money.
m
Every week I earned $100.
X
Y
4
900
After 4 weeks, I had $900.
How much did I start with?
Riddle
b
I started with some money.
m
Every week I earned $100.
X
After 4 weeks, I had $900.
1
Y
0
2
How much did I start with?
3
4
900
Riddle
b
I started with some money.
m
Every week I earned $100.
X
After 4 weeks, I had $900.
1
Y
0
2
How much did I start with?
3
800
4
900
Riddle
b
I started with some money.
m
Every week I earned $100.
X
After 4 weeks, I had $900.
1
How much did I start with?
Y
0
2
700
3
800
4
900
Riddle
b
I started with some money.
m
Every week I earned $100.
X
After 4 weeks, I had $900.
1
600
2
700
3
800
4
900
How much did I start with?
Y
0
Riddle
b
I started with some money.
$500
m
Every week I earned $100.
X
Y
0
500
After 4 weeks, I had $900.
1
600
2
700
3
800
4
900
How much did I start with?
900 – 400
4 * 100
Gained $400 Started with $500
“DRY”
Write the equation of the linear
relationship with:
m
m: 100
x y
point: (4, 900).
Y = mX + b
900 = 100(4) + b
900 = 400 + b
– 400
Y = 100X + 500
–400
500 = b
Ex. 1: Write the equation of a
line that goes through (7, 8) and
has a slope of 2.
Y = mX + b
NEED
m
and
Y = 2X – 6
b
NEED b!!!
How to use (7, 8)???
Input
X
Output
Y
Ex. 1: Write the equation of a
line that goes through (7, 8) and
has a slope of 2.
Y = mX + b
Y = 2X – 6
8 = 2(7) + b
8 = 14 + b
– 14 – 14
-6 = b
How to use (7, 8)???
Input
X
Output
Y
Ex. 2: Write the equation of a
line with this information:
m
slope: -5
X Y
point: (-4, 3)
Y = mX + b
3 is NOT
y-intercept!!!
Ex. 2: Write the equation of a
line with this information:
m
slope: -5
X Y
point: (-4, 3)
Y = mX + b
3 = -5(-4) + b
3 = 20 + b
– 20 – 20
-17 = b
Y = -5X – 17
Ex. 3: Write the equation of a line
that goes through (0, 8) and has a
slope of 2.
Y = mX + b
NEED
m
and
b
Y = 2X + 8
Ex. 3: Write the equation of a line
that goes through (0, 8) and has a
slope of 2.
Y = mX + b
NEED
m
and
b
Y = 2X + 8
Ex. 4: Write a rule from this information:
m
m: -4
X Y
point: (8, -2)
Y = mX + b
-2 = -4(8) + b
-2 = -32 + b
+ 32 + 32
30 = b
Y = -4X + 30
Ex. 5: Write an equation for a relationship
with this information:
m: zero.
point: (-4, -6)
Y = -6
The change in y
when x increases
by one
Ex. 6: Write an equation for a relationship
with this information:
m: undefined.
point: (-4, -6)
X = -4
The change in y
when x increases
by one
The End