Question

The height of a ball, in feet, that is thrown straight up and fall straight down is modeled by the quadratic function y = −16(x-1)^2 + 21 where x is time, in seconds. At the time the ball is thrown, how high is it above the ground?

The ball is thrown from 1 foot above the ground.
The ball is thrown from the ground.
The ball is thrown from 21 feet above ground.
The ball is thrown from 5 feet above ground.

Answer 1

For this equation, you'll need to set x to 0 and solve from there.

`y=-16(0-1)^2+21`

First step is to solve the parentheses and then square the answer. Your equation will look like this:
`y=-16*1+21`

Next, you will multiply -16 and 1, and then add the product of that by 21. Your answer will be
`y=5`

In short, the ball is thrown from 5 feet above ground.