Answer: undefined
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Step-by-step explanation:
Slope Formula
m = (y2-y1)/(x2-x1)
m = (-9-7)/(-4-(-4))
m = (-9-7)/(-4+4)
m = -16/0
We cannot divide by zero, so the slope is undefined.
All vertical lines have an undefined slope because any two points on this line will have x coordinates of the same value. Those x coordinates subtract to 0.