Question

The function f(t) = −5t 2 + 20t + 60 models the approximate height of an object
t seconds after it is launched. How many seconds does it take the object to hit the
ground?

Answer 1

Plug in f(t) = 0. We do this because f(t) represents the height and a height of 0 means you're at the ground. 

f(t) =-5t^2 + 20t + 60 

0 = -5t^2 + 20t + 60 

-5t^2 + 20t + 60 = 0 

Now solve for t using the quadratic formula