Question

A 10-foot ladder rests against a vertical wall. Let x be the distance from the bottom of the ladder to the wall and y be the distance from the floor to the top of the ladder. If the bottom of the ladder slides away from the wall, how fast does the top of the ladder fall down the wall with respect to x

Answer 1

The rate of change of the top of the ladder with respect to x is -x/y

Explanation:

The given parameters are;

The length of the ladder = 10 ft.

The horizontal distance of the bottom of the ladder from the wall = x

The distance of the top of the ladder from the floor = y

By Pythagoras's theorem, we have;

10 = y² + x²

Therefore, we have;

x² = 10 - y²

d(x²)/dx = 2·x = d(10 - y²)/dx = -2·y·dy/dx

∴ 2·x = -2·y·dy/dx

dy/dx = 2·x/(-2·y) = -x/y

Therefore, the rate of change of the top of the ladder with respect to x, dy/dx = -x/y.