Question

ashton drops a golf ball. its height at any time is given by the equation f(x)=20-5x^2 where x is the time elasped in seconds. when will the ball hit the ground?

Answer 1

set the height =0 and solve for x. So 0=-5x^2+20.
-20=-5x^2
4=x^2
x=+-sqrt(2)
since you only care about the positive root (no such thing as negative time, the answer is 2)

Plug in to check -5(2^2)+20=0
-5(4)=-20
-20=-20

Answer 2

thanks!