SOLUTION: WHy does a horizontal line have a slope of 0 when a vertical line has an undefined slope?

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Question 401621: WHy does a horizontal line have a slope of 0 when a vertical line has an undefined slope?
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Any two points on a horizontal line have coordinates (a, b) and (c, b). The slope is then equal to %28b-b%29%2F%28c-a%29+=+0%2F%28c-a%29+=+0, given a is not equal to b.
Any two points on a vertical line have coordinates (d, e) and (d, f) (assuming e not equal to f). The slope is then equal to %28f-e%29%2F%28d-d%29+=+%28f-e%29%2F0 = undefined, because division by 0 is impossible.