## anonymous one year ago find the axis of symmetry for this parabola y=-5x^2-10x-13

1. anonymous

write the answer as an equation

2. IrishBoy123

complete the square $$y=-5x^2-10x-13$$ might be easier to do it starting with this $$y=-5[x^2+2x+\frac{13}{5}]$$

3. anonymous

-1?

4. IrishBoy123

$$\large \checkmark$$

5. anonymous

It's not that

6. IrishBoy123

it is x = -1 if you copied the question correctly

7. anonymous

I copied the question right but -1 wasn't the answer

8. anonymous

try this one y=-x^2+6x-8

9. Loser66

@Kaelyn78 you want us do your homework, don't you?

10. IrishBoy123

11. anonymous

these are practice problems, not homework

12. anonymous

13. anonymous

and no I can't, I don't know how to find the axis of symmetry in my head

14. IrishBoy123

we still haven't finished the first one if the answer is not x = -1, what is it?!

15. anonymous

I don't know, that's why I posted it here.

16. anonymous

1 or -1

17. Loser66

The first one, @IrishBoy123 showed you all the steps + proof. You said it is not the right answer without any reason. I am with him and don't get why you go to other one without finish the first one. :)

18. IrishBoy123

do it another way $$y=-5x^2-10x-13$$ $$y' = -10 x - 10$$ $$y' = 0 \implies x = -1$$

19. anonymous

because I entered that answer into the computer and it said it isn't right

20. Astrophysics

Irish boy is right!

21. anonymous

Computers don't lie, and they don't give you an explanation of why it's wrong

22. anonymous

I came to the same conclusion he had, I agree with him, but the computer doesn't.

23. Astrophysics

You can check another way by finding the vertex, $x= -\frac{ b }{ 2a }$

24. Astrophysics

$x = - \frac{ (-10) }{ 2(-5) } = -1$

25. anonymous

Guys they don't give you an option to do the problem a second time. I entered the answer and it was wrong so I just have to move on to the next question. Proving it to me over and over again will not change anything.

26. anonymous

If you ever meet the developers of the program I'm working with you can argue with them about that. Thank you all for your help on that problem.

27. IrishBoy123

put each new question in a new thread and let's see if we can sort out that pesky computer of yours. perhaps you should wire it to a lie detector :p

28. Astrophysics

lool

29. anonymous

That would be great... Technology is great when it works, horrible when it doesn't