A ball is thrown into the air. The height h, in feet, of the ball can be modeled by the equation h = - 16t^2 + 20t + 6, where t is the time, in seconds, the ball is in the air. When will the ball hit the ground?

Hello : let h = f (t)

the ball hit the ground if : f (t) = 0

solve : - 16t² + 20t + 6=0

Δ = b²-4ac ... a = - 16 b = 20 c = 6

Δ = (20) ²-4 (-16) (6) = 784 = 28²

t1 = (-20-28) / - 32 = 48/32 = 3/2

t2 = (-20+28) / - 32 < 0 refused

conclusion : t=3/2