Originally Posted by

**joatmon** Can anybody show me how this

$\displaystyle \frac{-4x}{9\sqrt{4-\frac{4x^2}{9}}}$

winds up simplifying to this:

$\displaystyle \frac{-2x}{3\sqrt{9-x^2}}$

Here's what I have done, but I get a different answer:

$\displaystyle \frac{-4x}{9\sqrt{4-\frac{4x^2}{9}}}$

$\displaystyle \frac{-4x}{9\sqrt{36-4x^2}}$ Wrong

$\displaystyle \frac{-4x}{9\sqrt{4(9-x^2)}}$

$\displaystyle \frac{-4x}{9(2)\sqrt{9-x^2}}$

$\displaystyle \frac{-2x}{9\sqrt{9-x^2}}$

I just don't see how that 3 winds up in the denominator. I get a 9.

Thanks.