Posted by Sarah on .
A man 6ft. tall walks at the rate of 5 ft/sec toward a streelight that is 16 ft. above the ground. At what rate is the length of his shadow changing when he is 10ft. from the base of the light?

Calculus rates 
Damon,
x is shadow tip from streetlight
y is man from streetlight
from similar triangles
x/16 = (xy)/6
16 x  16 y = 6 x
16 y = 10 x
x = 1.6 y
dx/dt = 1.6 dy/dt
= 1.6*5