Question

A projectile is thrown upward so that its distance above the ground after t seconds is h = - 16t2 + 440t.. . After how many seconds does it reach its maximum height?

Answer 1

If y = ax^2 + bx + c, and a is negative, the maximum happens when x = -b / (2a). 

Here they have different variables but do it the same way: t = -640 / (2 • -16) 
= -640/-32 = 20 sec