1. Write an equation given two points
EXAMPLE 2
Write an equation given two points
Write an equation of the line that passes through (–2, 5) and (2, –1).
SOLUTION
STEP 1
Calculate the slope. 3
m =
y2 – y1
x2 – x1 =
–1 – 5
2 – (–2) –6 4 – 2
STEP 2
Find the y-intercept. Use the slope and the point (–2, 5).
y = mx + b
Write slope-intercept form.

2. Write an equation given two points
EXAMPLE 2
Write an equation given two points
5 = – 3 2
(–2)
+ b
Substitute – for m, –2 for x, and 5 for y. 3 2
2 = b
Solve for b.
STEP 3
Write an equation of the line.
y = mx + b
Write slope-intercept form.
y = – 3 2 x
+ 2
Substitute – 3 2
for m and 2 for b.

3. Standardized Test Practice
EXAMPLE 3
EXAMPLE 3
Standardized Test Practice
Which function has the values f(4) = 9 and f(–4) = –7?
f (x) = 2x + 10 A B
f (x) = 2x + 1 C
f (x) = 2x – 13 D
f (x) = 2x – 14
STEP 1
Calculate the slope. Write f (4) = 9 as (4, 9) and f (–4) = –7 as (–4, –7).
m =
y2 – y1
x2 – x1 =
–7 – 9
–4 – 4
–16 –8 2
STEP 2
Find the y-intercept. Use the slope and the point (4, 9).
y = mx + b
Write slope-intercept form.

4. Standardized Test Practice
EXAMPLE 3
Standardized Test Practice
9 = 2(4) + b
Substitute 2 for m, 4 for x, and 9 for y.
1 = b
Solve for b.
STEP 3
Write an equation for the function. Use function notation.
f (x) = 2x + 1
Substitute 2 for m and 1 for b.
ANSWER
The answer is B. A C D B

5. GUIDED PRACTICE
for Examples 2 and 3
2. Write an equation of the line that passes through (1, –2) and (–5, 4).
y = –x – 1
ANSWER

6. GUIDED PRACTICE
for Examples 2 and 3
3. Write an equation for the linear function with values
f(–2) = 10 and f(4) = –2?
y = –2x + 6
ANSWER