Post on 26-Mar-2015
Warm up
2
1
2
1
Write the equation of the line passing through the given point with the given slope. Then graph the line.
1. (-4, -3), m =
2. (8, 2), m =
answers
1. Y= ½ x – 1
2. Y= -½ x + 6
How do we use Two Points to Write an Equation?
Step 1: Find the slope.Step 2: Use one of the
points and your slope to solve for b.
Step 3: Write your equation in slope-intercept form using slope and y-intercept
Example
Write an equation for the line through these points. (-1,-5) and (-2, 3).
3 ( 5)
2 ( 1)m
8
1m
83 ( 2)
1b 3 16 b
3 16 16 16 b
13b 813
1y x
Your Turn:
Write an equation for the line through these points.
(1, 3) and (-1, -1)
(-1, 6) and (7, -10)
(10, -1) and (4, 2)
(-14, -2) and (7, 7)4
2
1 xy
47
3 xy
12 xy
42 xy
Write an equation of the line that has each pair of intercepts
x-intercept: (-3,0), y-intercept: (0,6)
)3(0
06
m 2m
b )3(20 b6
62 xy
Your Turn:
Write an equation of the line that has an x-intercept of (2,0) and a y-intercept of (0,-5).
20
05
m2
5m
b )0(2
55 b 5
52
5 xy
Part 2: How do write an equation using a table?
Step 1: Find the rate of change. (change in Y over change in X)
Step 2: Use either point and your slope to solve for b.
Step 3: Write your equation in slope-intercept form using slope and y-intercept
X Y
-1 4
3 6
5 7
11 10
2
9
2
1 xy
Your Turn:
Write in slope-intercept form.
X Y
-11 -7
-1 -3
4 -1
19 55
13
5
2 xy
Review Key Concepts
Slope-intercept Form• Y = mx + b
• Ex. Y=-½x + 5
Standard Form
• Ax + By = C
• Ex. 2x + 3y= 5
Summary:
Name the steps for writing an equation from two points?