Question

-4sqrt(x+9)=20 can anyone help?

Answer 1

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

Answer 2

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

Answer 3

and yes like that

Answer 4

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

Answer 5

yeah your probably right. extraneous solution?

Answer 6

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

Answer 7

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

Answer 8

\(\large{\sqrt{-x} = i \sqrt{x}}\) right?

Answer 9

yeah

Answer 10

Okay, can we use that somehow?

Answer 11

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

Answer 12

hmmm yeah

Answer 13

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

Answer 14

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

Answer 15

yeah it looks like that then and thanks man

Answer 16

Hey, no problem. :)