Question

How would you do this problem?

Answer 1

6 seconds

Explanation:

First: equalize the equation to zero

f(t) = -5t² + 20t + 60

-5t² + 20t + 60 = 0

Second: find its roots

-5(t² - 4t - 12) = 0

-5 (t - 6)(t + 2) = 0

`t - 6 = 0 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: t + 2 = 0 \\ t = 6 \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: \: t = - 2`

Time can't be negative so the answer is: it takes 6 seconds to hit the ground

Answer 2

f(x)=-5t^2+20t+60
Divide everything by -5
f(x)=t^2-4t-12
(t-6)(t+2)
Set it up to zero
t-6=0. t+2=0
t=6. t=-2
Since you can’t have negative seconds, the answer is 6 seconds