calculus
posted by theo .
A piece of land is shaped like a right triangle. Two people start at the right angle at the same time, and walk at the same speed along different legs of the triangle while spraying the land. If the area covered is changing at 4m^2/s how fast are the people moving when they are 5m from the right angle? (Round
approximations to two decimal places.)

length of side = v t
a = area = .5 (vt)^2 = .5 v^2 t^2
da/dt = (.5 v^2)(2 t) = v^2 t
4 = v^2 t
v t = 5
4 = 5 v
v = 4/5