A kite is 60 ft high with 100 ft of cord out. If the kite is moving horizontally 4 mi/hr directly away from the boy flying it, find the rate of change of the angle of elevation of the cord.
when s = 100 ft
When s = 100 ft
x = 80 ft (see Solution 45 above)
cos θ = 80/100 = 4/5