$\displaystyle lim_{x \to a} \dfrac{\sqrt{2a^3x-x^4}-a\sqrt[3]{a^2x}}{a-\sqrt[4]{ax^3}}$

Really no idea where to start with this. I think what's throwing me off is the a's. I know that they are constants but having a bit of trouble figuring out how to deal with them.

I can get this far.. and I'm not even sure if it's right or not.

$\displaystyle lim_{x \to a} \dfrac{(2a^3x-x^4)^{1/2} - a(a^2x)^{1/3}}{a - (ax^3)^{1/4}}$

$\displaystyle lim_{x \to a} \dfrac{\dfrac{2a^3-4x^3}{\sqrt{2a^3x-x^4}}-\dfrac{a^3}{3(a^2x)^{3/4}}}{-\dfrac{3\sqrt[4]{ax^3}}{4x}}$