Question

A ladder 25 feet long is leaning against the wall of a house. The base of the ladder is pulled away from the wall at a rate of 2 feet per second. How fast is the top of the ladder moving down the wall when its base is 7 feet?

Answer 1

x^2+y^2 = 25

x dx/dt + y dy/dt = 0

So, find y when x=7, and then just use your numbers to find dy/dt

Answer 2

-14/24 = dy/dt?

Answer 3

Looks good to me, but I'd write it as

-7/12 ft/s