#1**+10 **

$$\\It\; is\; 100-4x^2\\\\

\mbox {But this is not one of the answers so we need to look some more}\\

100=10^2\\

4x^2=(2x)^2\\

\mbox{So we have a difference of two squares}\\

100-4x^2=(10-2x)(10+2x)\\

\mbox{So the answer is c}\\$$

Melody Aug 5, 2014

#3**+10 **

Because you had a square peice of paper 10cm * 10cm. That was 100cm^2

then you cut a square out of each of the 4 corners that was [xcm * xcm]*4 = 4x^2 cm^2

so you were left with [100-4x^{2}] cm^{2 }of paper

You need to give this question a title please.

Melody Aug 5, 2014