Question

PLEASE HELP ME I ONLY HAVE 20 MINUTES!!!!

The height of a tennis ball
tossed into the air is modeled by h(x) = 40x -16x^2, where x is elapsed time in seconds. During what time interval will the tennis ball be at least 15 feet above the ground?

I’m pretty sure it’s D but I need an explanation why!!!

Answer 1

`h(x) = 40x - 16x^2\\h(x) = 15\\40x - 16x^2 = 15\\-16x^2 + 40x - 15 = 0\\`

Using the quadratic formula we get

`x_1 = 0.5\\x_2 = 2.04`

Therefore the tennis ball is at least 15 feet above the ground from 0.5 seconds to 2.04 seconds