Question 951227
A professional stunt diver jumps off a tower.
 His height above the ground is given by the expression h(t)=-5t^2+20.
 How long does it take for the diver to reach the water? 
:
When he strikes the water his height is 0, therefore
-5t^2 + 20t = 0
simplify, divide by -5t
t - 4 = 0
t = 4 seconds