Name:__________________________________________ Date:______________________ Period:________
Algebra 2
Section 2-4 Day 2
More About Linear Equations
Writing Equations of Lines
The 3 forms of an equation of a line are:
Slope-Intercept Form
Point-Slope Form
Standard Form
y  mx  b
y  y1  m( x  x1 )
Ax  By  C
Use this form when you know the
Use this form when you know the
A, B, and C are real numbers. A
______________ and the
_____________ and a _________,
and B cannot both be
__________________.
or when you know ____________.
_____________.
What is the equation of the line y 
y
3
x  5 in standard form? Use integer coefficients.
4
3
x5
4
Write the equation of a line in standard form with integer coefficients.
1. y 
1
x2
2
2. y  7 x  9
3. y 
3
x3
5
4. y  4.2  7.9
To write the equation of line:
Pick the form that matches the information you are given { y  mx  b or y  y1  m( x  x1 ) }
Substitute given information into the corresponding equation
Solve equation for the appropriate form in the directions
Given two points:
o Find the slope
o Pick a point
o Use point-slope to write the equation of the line
 Given a graph:
o Find your y-intercept (b) and slope (m)




Examples:
I. Write an equation of the line in slope-intercept form of each line described.
1. slope 2; y-intercept 15
____________________
1
2
2. slope  ; y-intercept
3
2
____________________
3. slope –3, (–1, 2)
____________________
II. Write an equation of the line in standard-form form of each line described.
4. slope 0 , through (1, –4)
____________________
5. (4, –3) and (3, –6)
____________________
6. vertical line through (9, –15)
____________________
III. Write an equation of the line in point-slope form of each line described.
7. slope 
1
, through (2, –5)
4
8. (5, –12) and (0, –6)
____________________
9. horizontal line through (1, 2)
____________________
____________________
Write an equation of the line in slope-intercept form of each line graphed.
10.
11.
___________________
12.
___________________
____________________
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Writing Equations of Lines