a firecracker is fired from the ground. The height of the firecracker at a given time is modeled by the function h(t) =-5t^2+50t, where h(t) is the height in metres and t is the time in seconds. When will the firecracker reach a height of 45m ?

Answer 1

solve for t in

45 = -5t^2 + 50t
5t^2 - 50t + 45 = 0
t^2 - 10t + 9 = 0
(t-9)(t-1) = 0

it will reach 45m on the way up at t=1, and on the way back down at t=9.