find the time it take the flare to hit the ground

Question

the height of a flare can be approximated by the function h=-t²+5t+6, where h is the height in feet and t is the time in seconds. Find the time it takes the flare to hot the ground.

Answer 1

Set h = 0 and solve for t.

 

-t² + 5t + 6 = 0

 

t² - 5t - 6 = 0

 

(t - 6)(t + 1) = 0

 

Time must be positive, so the solution is

 

t = 6s.