# Word Problem

### Quadratic formula, Mr. Kirkland, 10-16-13

We are going to solve this cannonball equation by using the Quadratic Formula. We use the Quadratic Formula to find the x-intercepts.

y=-b+-√b^2-4(a)(c)/2(a)

If a cannon is fired from 7 feet off the ground and the flight path is modeled by y=-16t^2+85t+7, how long does it take for the cannonball to hit the ground?

-16t^2+85+7 A=-16 B=85 C=7

-85+-√85^2-4(-16)(7)/2(-16)

-85+-√7225+448/-32

-85+-√7673/-32

-85+√7673/-32 -85-√7673/-32

x=-0.81, 5.39

5.39 seconds