
Arturo O. answered 01/31/17
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When two lines of slope m1 and m2 are perpendicular, m1m2 = -1.
Let m1 = 5. Then any line of slope m2 ≠ -1/5 is not perpendicular to a line of slope 5.
Here are 3 examples:
y = 6x
y = 7x - 13
y = 5x + 90
There are infinitely many more.