A ladder 20 feet long leans against a vertical building. If the bottom of the ladder slides away from the building horizontally at a rate of 3...

Let `x` be
the distance from the wall, and let `y` be the height at the top of the ladder.

Then from the pythagorean theorem we have `x^2+y^2=20^2` .

We are
given that the rate of change of the bottom of the ladder away from the wall is
3ft/sec,...

href="https://en.wikipedia.org/wiki/Related_rates">https://en.wikipedia.org/wiki/Related_rates