A projectile is thrown upward so that its height above the ground after t seconds is given by the function:
After how many seconds does the projectile take to reach its maximum height?
I'll assume that you are not familiar with Calculus.
The graph of is a down-opening parabola.
Its maximum is at its vertex.
The formula for the vertex is: .
We have: .
The projectile takes 18 second to reach maximum height.
[The maximum height is: . units.]