1. Do Now 11/15/11 Line 1: (2, -7) (0,-5) Line 2 (0, 4), (8, 3.5)
In your notebook, explain how you find the equation for a line when given two points. Then find the equation of the following two lines.
Line 1: (2, -7) (0,-5)
Line 2 (0, 4), (8, 3.5)
y = -x – 5
y = -1/16x + 4

2. Objective
write equations of lines using points on the line.

3. Section 5.2 “Use Linear Equations in Slope-Intercept Form”
a linear equation written in the form
y-coordinate
x-coordinate
y = mx + b
slope
y-intercept

4. Writing an Equation Using Slope-Intercept Form
Step #1
Identify slope.
Step #2
Find the y-intercept. Substitute the slope and the coordinates of a point (x,y) on the line y = mx + b. Then solve for b.
Step #3
Write the equation using y = mx + b

5. Write an equation of the line that passes through the point (– 1, 3) and has a slope of – 4.
STEP 1
Identify the slope. The slope is – 4.
STEP 2
Find the y-intercept. Substitute the slope and the coordinates of the given point in y = m x + b. Solve for b.
y = m x + b
Write slope-intercept form.
3 = – 4(– 1) + b
Substitute – 4 for m, – 1 for x, and 3 for y.
– 1 = b
Solve for b.
STEP 3
Write an equation of the line.
y = m x + b
Write slope-intercept form.
y = – 4x – 1
Substitute – 4 for m and – 1 for b.

6. Write an equation of the line that passes through the point (6, 3) and has a slope of 2.
STEP 1
Identify the slope. The slope is 2.
STEP 2
Find the y-intercept. Substitute the slope and the coordinates of the given point in y = m x + b. Solve for b.
y = m x + b
Write slope-intercept form.
3 = 2(6 ) + b
Substitute 2 for m, 6 for x, and 3 for y.
– 9 = b
Solve for b.
STEP 3
Write an equation of the line.
y = m x + b
Write slope-intercept form.
y = 2x – 9
Substitute 2 for m and – 9 for b.

7. Write an equation of the line that passes
through (– 2, 5) and (2, – 1).
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). Solve for b.
y = m x + b
Write slope-intercept form.
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 = m x + b
Write slope-intercept form.
y = – 3 2 x
+ 2
Substitute – 3 2
for m and 2 for b.

8. Write an equation of the line that passes
through (1, 4) and (2, 7).
STEP 1
Calculate the slope. 3
m =
y2 – y1
x2 – x1 =
7 – 4
2 – 1 1
STEP 2
Find the y-intercept. Use the slope and the point (2, 7). Solve for b.
y = m x + b
Write slope-intercept form.
7 = 3 1
( 2)
+ b
Substitute for m, 2 for x, and 7 for y. 3 1
1 = b
Solve for b.
STEP 3
Write an equation of the line.
y = m x + b
Write slope-intercept form.
y = 3 1 x
+ 1
Substitute 3 1
for m and 1 for b.

9. Slope-Intercept Form Summary
When given:
(1) slope and y-intercept
Substitute into equation
(2) slope and one point
Substitute m and the coordinates of the point in y = mx + b. Then solve for b.
(3) two points
Use the 2 points to find the slope. Then substitute m and the coordinates of the point in y = mx + b. Then solve for b.

10. With your tribe, work on the “Real-Life” applications Bald Eagle worksheet.

11. Algebra in “Real-Life!”
In your groups, complete the two “real-life” activities.
Interdisciplinary Application “Bald Eagles”
1) y = 393x + 14,324
2) graph
3) approximately 18,254
4) habitat loss, less people counting
5) y = x + 13,698
6) graph
7) approximately 18,880