Thread: Quadratic Problem Help

Thanks for your help in advance, here's the problem:

The path of a golf ball can be modeled by a quadratic equation. The path of a ball hit an angle of 10 degrees can be modeled by h=-0.002d^2+0.4d where h is the height in meters and d is the horizontal distance the ball travels in meters until it first hits the gorund.

a) What is the maximum height reached by the ball?


The answer is 20m, usually I would just sub in 0 for d to find h but in this case it's different. What should I do?

Hello, andi01!

The path of a golf ball can be modeled by a quadratic equation.
The path of a ball hit an angle of 10° can be modeled by:
where is the height in meters and is the horizontal distance.

a) What is the maximum height reached by the ball?

The answer is 20m.
Usually I would just sub in 0 for d to find h. . . Why?

Think of what you said . . .

You let .
The ball has not moved yet.
What is its height?
. . Obviously it's still on the ground!


Here's one way of looking at it:

The graph of is a down-opening parabola:

Its maximum is at its vertex.
The vertex is at: .

The maximum height is: . m.