Originally Posted by

**mark1950** Hmm...okay but what I actually did was this:

from

$\displaystyle =\frac{\sqrt{1+2x}(-2x) - (1-x^2)\frac{1}{\sqrt{1 + 2x}}}{1 + 2x}$

I equated the denominator of the numerator of the above to $\displaystyle \sqrt{1 + 2x}$ to become

$\displaystyle =\frac{\frac{(\sqrt{1 + 2x})(-2x)(\sqrt{1 + 2x}) - (1 - x^2)}{\sqrt{1 + 2x}}}{1 + 2x}$

then, simplifying them, I get

$\displaystyle =\frac{(-2x)(1 + 2x) - (1 - x^2)}{\sqrt{1 + 2x}} \times \frac{1}{1 + 2x} $

Is it against the math logic if I equate the denominator of the fractions in the numerator of the expression?