# equation w. radicals and exponenets

• Aug 12th 2011, 08:20 PM
mathmathmathmathmathmathm
$\sqrt{2x+2}-\sqrt{x-3}=2$

$\left(\sqrt{2x+2}\right)^{2}=\left(2+\sqrt{x-3}\right)^{2}$

$x+1=4\sqrt{x-3}$

i dont know where to go from here, i tried dividing by 4 and mult. the left by itself, and get lost, the answer is 7
• Aug 12th 2011, 09:33 PM
Prove It
Re: equation w. radicals and exponenets
Quote:

Originally Posted by mathmathmathmathmathmathm
$\sqrt{2x+2}-\sqrt{x-3}=2$

$\left(\sqrt{2x+2}\right)^{2}=\left(2+\sqrt{x-3}\right)^{2}$

$x+1=4\sqrt{x-3}$

i dont know where to go from here, i tried dividing by 4 and mult. the left by itself, and get lost, the answer is 7

\displaystyle \begin{align*} \sqrt{2x+2} - \sqrt{x-3} &= 2 \\ \sqrt{2x+2} &= 2+\sqrt{x-3} \\ \left(\sqrt{2x+2}\right)^2 &= \left(2+\sqrt{x-3}\right)^2 \\ 2x+2 &= 4 + 4\sqrt{x-3} + x - 3 \\ x + 1 &= 4\sqrt{x-3} \\ (x + 1)^2 &= \left(4\sqrt{x-3}\right)^2 \\ x^2 + 2x + 1 &= 16(x - 3) \\ x^2 + 2x + 1 &= 16x - 48 \\ x^2 - 14x + 49 &= 0 \\ (x - 7)^2 &= 0 \\ x - 7 &= 0 \\ x &= 7 \end{align*}
• Aug 13th 2011, 04:52 AM
HallsofIvy
Re: equation w. radicals and exponenets
You should of course, check the solution. (Squaring both sides of an equation may introduce "extraneous" solutions.)

$\sqrt{2(7)+ 2}= \sqrt{14+ 2}= \sqrt{16}= 4$
$\sqrt{7- 3}= \sqrt{4}= 2$

4- 2= 2 so the solution checks.
• Aug 13th 2011, 07:09 AM
mathmathmathmathmathmathm
Re: equation w. radicals and exponenets
thanks so much prove it, but can you explain when you get the (x-7) squared, how do you elimate the second (x-7) in the last step? does it cancel itself out? dont understand that step, thanks again
• Aug 13th 2011, 07:18 AM
Prove It
Re: equation w. radicals and exponenets
Quote:

Originally Posted by mathmathmathmathmathmathm
thanks so much prove it, but can you explain when you get the (x-7) squared, how do you elimate the second (x-7) in the last step? does it cancel itself out? dont understand that step, thanks again

To undo a square, you need to square root both sides. The square root of 0 is 0.