# 8x out of nowhere?

• Jan 22nd 2013, 04:25 PM
zsf1990
8x out of nowhere?
I'll admit it now: I understand most math and the concepts behind it. Regardless, I have much to improve upon when it comes to applying it and often make lots of stupid little mistakes.

So in this problem, can someone please tell me where the 8x comes from in the third line? It makes absolutely no sense to me. I'm sure it's another obvious detail I'm overlooking, lol.

http://c811129.r29.cf2.rackcdn.com/se0ae01135.png

• Jan 22nd 2013, 04:41 PM
abysmalgnat
Re: 8x out of nowhere?
(X-4)^2=x^2-8x+16
• Jan 22nd 2013, 04:47 PM
Soroban
Re: 8x out of nowhere?

Hello, zsf1990!

Don't tell me you think that $(x-4)^2$ is equal to $x^2+16$ !

. . $(x-4)^2 \;=\;(x-4)(x-4)$

Multiply it out!

• Jan 22nd 2013, 05:43 PM
zsf1990
Re: 8x out of nowhere?
I wasn't treating the right hand side as a factor. Like I said, foolish mistakes. That doesn't change how stupid I feel...