A golf ball is hit from the ground and represented by the equation ​ h(t)=−16t^2+64t+80 ​where h(t) is the height after t seconds. How long does it take for the golf ball to this the ground?

Answer 1

set the height equation = 0 if 0 is the ground level

-16t^2 + 64t + 80 = 0

divide by -8 to simplify

2t^2 -8t -10 = 0

divide by 2 to simplify more

t^2 -4t - 5 = 0

factor

(t-5)(t+1) = 0

set each factor = 0

t=5, t=-1; ignore the negative root

t=5 seconds before the ball hits the ground