slope intercept form & graphing definition - intercepts x-intercept y-intercept back the...
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Slope Intercept Form &
Graphing
Definition - Intercepts
x-intercept
y-intercept
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• The x-intercept of a straight line is the x-coordinate of the point where the graph crosses the x-axis.
• The y-intercept of a straight line is the y-coordinate of the point where the graph crosses the y-axis.
x
y
-4
1-3 -2 2 3-1
-2
-1
5
4
3
2
1
0
-5
-3
What is the y-intercept?
b = 3
b = -4
b = -3
b = 5
b = 0
y = mx + b
Slope-Intercept Form
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slopem interceptyb
y = 5x + 2
slope5 intercept2 y
Slope is Rise over Run.
• The numerator tells you to go up or down Positive = Up, Negative = Down.
•The denominator tells you how far to run left or right. Positive = Right, Negative = Left.
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3
1Up 1, Right 3.
1
2
Up 2, Left 1.
3
2 Down 2 Right 3 or
Up 2, Left 3BACK
Finding the slope and y-intercept
State the slope and y-intercept of:
y = 3x + 2BACK
Up/Down Left/Right
• The slope is 3 or 3/1 which means up 3 and right 1.
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y = 3x + 2
Slope = 3/1y-intercept= 2
Up 3 and Right 1
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When am I ever going to use this?
y = -2x + 3
Slope = -2/1y-intercept= 3
Down 2 and
Right 1BACK
y = 3x -2
You try this one
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y = 3x -2
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Changing equations to the form y = mx + b
•When equations are in the form ax + by = c, then you need to change them to y = mx + b
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Changing equations to the form y = mx + b
842 yx82422 xyxx824 xy
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4
82
4
4
xy
24
2
xy 2
2
1
xy
2x + 4y = 8 changed to y = -1/2x + 2
y-intercept= 2
Slope = -1/2
Down 1 Right 2BACK
Now you change 2x + 3y = 6 to y = mx + b
632 yx62322 xyxx
623 xy
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3
62
3
3
xy 23
2
xy
2x + 3y = 6 changed to y = -2/3x + 2
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Parallel Lines
43 xy23 xy
Same or different
The equations of two parallel lines have the same slope, but two different y-intercepts.
y = 3x + 4 and y = 3x - 2
y = 3x + 4
y = 3x -2
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What if there is no constant?
• If you have a problem like: y = 3x
• You can add a zero, “+ 0”, to the equation without changing the value.
03 xyBACK
Hints• If y = x + 3,the coefficient of x is
1, so the slope is 1/1.• If you do not have room to graph
a slope of 2/1 you can use the equivalent fraction -2/-1
intercept""0 yy
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Slope Intercept Form &
Graphing
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