## anonymous one year ago If a football player passes a football from 4 feet off the ground with an initial velocity of 36 feet per second, how long will it take the football to hit the ground? Use the equation h = −16t2 + 36t + 4. quantity of 9 plus or minus square root of 65 all over 8 9 plus or minus square root of 65 end root over 8 quantity of 9 plus or minus square root of 97 all over 8 9 plus or minus square root of 97 end root over 8

1. anonymous

You need to find time $$t$$ when the ball is at height $$h(t) = 0$$, i.e. solve the quadratic equation$-16t^2+36t+4 = 0$Can you do that?

2. anonymous

Notice that there is a common factor of 4. First thing I would do is factor out the 4. Then apply the quadratic formula to get your answer.

3. anonymous

is it a?

4. anonymous

How did you get a?

5. anonymous

sim-36+-square root of (36)^2 -4(16)(4)/2(16)

6. anonymous

simplify 36/32

7. anonymous

OK but then it will need to be simplified by factoring out common factors. It is easier to do this beforehand. simplify$-16x^2+36x+4=0$by factoring out a common factor of 4

8. anonymous

Hello?

9. anonymous

ok so the answer is 9 square root 65 all over 8

10. anonymous

Not quite. I assume you've factored out the 4 to get$-4x^2 + 9x + 1 = 0$Now apply the quadratic formula with a=-4, b=9, and c=1.

11. anonymous

$x=\frac{ -9 \pm \sqrt{9^2-4(-4)(1)} }{ 2(-4) } = ?$

12. anonymous

is it the whole thing over 8?

13. anonymous

-9+-square root of 97/

14. anonymous

-8

15. anonymous

@ospreytriple

16. anonymous

Very good. Now you a negative divide by a negative. So it can be simplified a tiny bit more to get your final answer.