- anonymous

Solve for x?

- schrodinger

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- anonymous

\[-4\sqrt{x+9}=20 \]

- anonymous

sqrt(x+9)=-(20/4)

- anonymous

I know how to solve is, I'm just not sure how to get rid of the -4 in the front of the radical.

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## More answers

- anonymous

you need to remove the square from x+9 the way you do that is by squaring both side and you end up with x+9=-(20/4)^2. then solve from there.

- anonymous

yes that 's it

- anonymous

x+9=-20/4)^2. -20/4^2 = -25 then take -25 subtract 9. you will get the answer of x=-34

- anonymous

it's easy to see that this has NO SOLUTION:
(-4)*(-5) = 20
so that means:
\(\large -4\sqrt{x+9}=20 \rightarrow \sqrt{x+9}=-5\)
\(\large \sqrt{x+9}=-5\)
which has no solution because the left side is always positive but the right side is negative

- anonymous

Can't you just square both sides to get rid of the square root, then solve like an equation?

- anonymous

yes you can try to do that... it's one technique you should try to solve it. but why continue when you know this is an impossible equation to solve?

- anonymous

not impossible, no solution...
if you do solve it, the solution is an extraneous solution....

- anonymous

If according to your answer it is √x+9 = -5 then you'd square both sides to have:
x+9 = -25
subtract 9 from both sides
and get -16 as x?

- anonymous

Difficult equation in history

- anonymous

squaring both sides you get positive 25

- anonymous

Oh, that's right thanks
so then x+9=25
subtract 9
then positive 16?

- anonymous

yes... now let's see if the solution of x=16 works....

- anonymous

no no no no =-20

- anonymous

that's wrong

- anonymous

\(\large (-4)(\sqrt{x+9})=20 \)
\(\large (-4)(\sqrt{\color {red}{16}+9})=20 \)
\(\large (-4)(\sqrt{\color {red}{25}})=20 \)
\(\large -4 \cdot 5 = 20 \)
\(\large -20=20 \) ???? not a true statement

- anonymous

so the solution of x=16 is extraneous and not really a solution.

- anonymous

solution \[\left| -4 \right|\]

- anonymous

suggestion hhhh

- anonymous

@AntarAzri , what's the solution?

- anonymous

\[\left| -4 \right|\]

- anonymous

\(\large (-4)(\sqrt{x+9})=20 \)
\(\large (-4)(\sqrt{|-4|+9})=20 \)
\(\large (-4)(\sqrt{4+9})=20 \)
\(\large (-4)(\sqrt{13})=20 \)
x=|-4| doesn't seem to work. That's not a solution.

- anonymous

my oh my I have headaches because of this problem..

- anonymous

no no i dont mean the x
|−4|=4

- anonymous

ok. whatever... my answer stands... NO SOLUTION to the equation:
\(\large (-4)(\sqrt{x+9})=20 \) \)

- anonymous

\[(\left| -4 \right|)(\sqrt{16+9})=20\]

- anonymous

here's wolframs answer:
http://www.wolframalpha.com/input/?i=solve+-4*sqrt%28x%2B9%29%3D20

- anonymous

good

- anonymous

http://www.wolframalpha.com/input/?i=solve+|%E2%88%924|*sqrt%28x%2B9%29%3D20

- anonymous

?

- anonymous

if u don't understand my answer and expanation maybe someone else can give u a better answer... i will not argue my point further....

- anonymous

Do we agree that it can not be the root of a negative number gives a positive number ?

- anonymous

I'll see what my teacher says when she grades it. Thanks for your time

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