Five-Minute Check (over Lesson 8–7)

Then/Now

New Vocabulary

Example 1: Write the Equation of a Line in Slope- Intercept Form

Example 2: Write an Equation Given Two Points

Example 3: Write an Equation from a Table

Example 4: Real-World Example: Write an Equation to Make a Prediction

Concept Summary: Write a Linear Equation

Over Lesson 8–7

A. slope = 2; y-int = 5

B. slope = 1; y-int = 5

C. slope = 1; y-int = –5

D. slope = 2; y-int = –5

Find the slope and y-intercept for the graph of y = x + 5.

Over Lesson 8–7

A. slope = ; y-int = –3

B. slope = 2; y-int = –3

C. slope = 2; y-int = 3

D. slope = ; y-int = 3

Find the slope and y-intercept for

Over Lesson 8–7

A. slope = 1; y-int = 4

B. slope = 1; y-int = –4

C. slope = –1; y-int = –4

D. slope = –1; y-int = 4

Find the slope and y-intercept for the graph of x + y = 4.

Over Lesson 8–7

Graph y = 3x + 1 using the slope and y-intercept.

A. B.

C. D.

You have already graphed linear equations using the slope and y-intercept. (Lesson 8–6)

• Write equations given the slope and y-intercept, a graph, a table, or two points.

• Use linear equations to solve problems.

• point-slope form

y – y1 =m(x – x1)

Write the Equation of a Line in Slope-Intercept Form

y = mx + b Slope-intercept form

Answer:

A. Write an equation in slope-intercept form for the

line with slope and y-intercept 7.

Write the Equation of a Line in Slope-Intercept Form

B. Write an equation in slope-intercept form for the line graphed.

The y-intercept is –4. From (0, –4), you can go up one unit and to the right one unit to another point on the line. So, the slope is 1.

Write the Equation of a Line in Slope-Intercept Form

y = mx + b Slope-intercept form

Answer: y = x – 4

y = 1x + (–4) Replace m with 1 and b with –4.

y = x – 4 Simplify.

Write an Equation Given Two Points

Write an equation for the line that passes through the points (7, 0) and (6, 3).

Step 1 Find the slope m.

Definition of slope

(x1, y1) = (7, 0)

(x2, y2) = (6, 3)

Simplify.

Write an Equation Given Two Points

Step 2 Use the slope and the coordinates of eitherpoint to write the equation in point-slope form.

y – y1 = m(x – x1) Point-slope form

y – 0 = –3(x – 7) Replace (x1, y1) with (7, 0) and m with –3.

y = –3x + 21 Simplify.

Answer: y = –3x + 21

Write an equation for the line that passes through (4, –2) and (–2, –14).

A. y = –8x + 30

B.

C. y = 2x + 6

D. y = 2x – 10