Question

A projectile is thrown upward so that its distance above the ground after t seconds is given by the function h(t) = -16t2 + 704t. After how many seconds does the projectile take to reach its maximum height?

Answer 1

You need to find the x-coordinate (h) of the vertex of the parabola.

$-16t^2+704t=0\\ h=-\dfrac{b}{2a}=-\dfrac{704}{2\cdot(-16)}=22$

After 22 seconds.