## anonymous 3 years ago -4sqrt(x+9)=20 can anyone help?

1. anonymous

$-4 \sqrt{(x+9)} = 20$ Like this? At what part are you getting stuck?

2. anonymous

well i get x=16 but when i try to see if its true i get -20=20

3. anonymous

and yes like that

4. anonymous

Yeah, with that -4 outside the square root, I think it's undefined.

5. anonymous

yeah your probably right. extraneous solution?

6. anonymous

If we defined $$y$$ as $$\sqrt{(x+9)}$$, we would get $$-4y = 20$$, with $$y = -5$$, and there is no way $$\sqrt{(x+9)} = -5$$

7. anonymous

hmmm i dont know. but when we divide -4 we get $\sqrt{x+9}=-5$

8. anonymous

$$\large{\sqrt{-x} = i \sqrt{x}}$$ right?

9. anonymous

yeah

10. anonymous

Okay, can we use that somehow?

11. anonymous

Oh wait... We can square both sides, right?

12. anonymous

hmmm yeah

13. anonymous

and we get x+9=25 because -5x-5=25

14. anonymous

Right, so you were right with 16; it is an extraneous root.

15. anonymous

yeah it looks like that then and thanks man

16. anonymous

Hey, no problem. :)