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5-1(Part 1)
Write Linear Equations in Slope-Intercept Form
Big Idea:
-Verify that a point lies on a line, given the equation of the line.
-Derive linear equations by using the point-slope formula.
Recall:
 The graph of an equation in slope-intercept form,
y = mx + b, is a line with a slope of m and a yintercept of b.
 You can use this form to write an equation of a
line if you know its slope and y-intercept.
Example:
 Write an equation of a line with a slope of 4 and a y-
intercept of -3.
 Solution:
y  mx  b
 Now substitute 4 for m and -3 for b.
y  4x  3
Extra Examples: Write an equation:
1. Slope is 8; y-intercept is -7
3
2. Slope is
; y-intercept is -3
4
Using Two Points
If you know the point where a line crosses the yaxis and another point on the line, you can
write an equation of the line.
Ex 1: Write an equation of the line
shown:
Step 1: Calculate slope:
m=
y
10
9
8
7
6
5
4
3
2
1
x
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
-1
-2
-3
-4
(0, -5)
-5
Step 2: Write an equation of
the line:
y=
-6
-7
-8
-9
-10
1
2
3
4
5
6
7
(3, -1)
8
9 10
Ex 2: Write an equation of the line
shown:
Step 1: Calculate slope:
(3, 3)
m=
y
10
9
8
7
6
5
4
3
2
1
x
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1
-1
(0, -2)
-2
-3
-4
-5
Step 2: Write an equation of
the line:
y=
-6
-7
-8
-9
-10
1
2
3
4
5
6
7
8
9 10
Using Two Points Only! (No Graph)
You can write the equation of a line given two
points by:
1. Calculating the slope
2. Identifying the y-intercept
3. Using y = mx + b
Examples: Write an equation of the
line containing the points:
(1) (0, -2) and (8, 4)
Find the slope:
m=
Identify the y-intercept:
b=
Write the equation of the line:
y = mx + b
Examples: Write an equation of the
line containing the points:
(2) (-3, 6) and (0, 5)
(3) (0, 3) and (-4, 11)
(4) (-6, 0) and (0, -24)