Mary Ann F. answered • 01/07/15

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Math & Science... Algebra and Geometry specialist

Can you see that these are (x,y) ordered pairs?

(0,20)

(2,18)

(4,16)

(8, 12)

You could figure the slope between any two of these points.

Slope = rise/run = Δy/Δx = y2 - y1

x2 - x1

e.g.) 18 - 12 = 6 = -1

2 - 8 -6

slope = -1

We know the y intercept because the point (0,20) is given.

So I can write the equation that includes all these points using

y intercept form y = mx + b: y = -x +20

The rule is "take the opposite (or the negative) of your input value and then add 20".