1. [SOLVED] Easy Factoring Question?

Please forgive me, but I am having a total mind block..

I am doing a question about a diver, and I have to determine when the diver hits the water. The equation is y= -5t^2 +10t +50.

I have tried simple factoring, complex factoring, and using the quadratic formula and nothing has worked =( Don't know whats going on. I know the answer is 4.3 something through my graphing calculator, but I can't get there.. I have done many questions like this before but I have been sitting here for half an hour trying to figure this one out, and I either did something wrong or I am missing something simple and stupid because I've been doing math all day.

Thanks

2. What may help in that particular problem is to factor out the 5 and then trying to complete the square. That method should at least be a step in the right direction i hope!

3. Ahhh, well I will have to review how to complete the square then :/

4. _____________________
= -10 + / 10^2 - 4(-5)(50)
_________________________
2(-5)

= - 10 + 33.17
_____________

-10

Survery Says:

= -2.37 or 4.42

Sorry it doesnt look pretty, but thats what happens when you have limited resources in a computing lab.

5. Ahhh, I figured out why. I inputted a -5 in the -b at the beginning instead of a 10 :/ stupid mistake. I really should learn how to complete the square though

6. Originally Posted by Slipery
Ahhh, I figured out why. I inputted a -5 in the -b at the beginning instead of a 10 :/ stupid mistake. I really should learn how to complete the square though
completing the square would give

$\displaystyle y= -5t^2 +10t +50$

$\displaystyle y=-5(t^2-2t)+50$

$\displaystyle y=-5(t^2-2t-1+1)+50$

$\displaystyle y=-5(t^2-2t)+50+5$

$\displaystyle y=-5(t^2-2t)+55$

$\displaystyle y=-5(t-1)^2+55$

$\displaystyle V1,55)$