Rules for cancelling fractions with exponents I have an expression that I need to simplify, I know the answer (wolframalpha) but I'm not sure of the rule that gets me there. 
$\dfrac{(\alpha) X_1^{\alpha -1} X_2^{1-\alpha}}{(1-\alpha)X_1^\alpha X_2^{-\alpha}}$
Basically I know that on the $X_1$ side of the fraction it cancels down to $\frac{1}{x_1}$ and the $X_2$ side cancels to $\frac{x_2}{1}$ leaving me with the alphas still outside and $\frac{X_2}{X_1}$. 
But I don't know the exponent rule that allows me to do this cancellation. I just want to be sure I understand it fully. 
Thanks. 
Edit: Thank you very much to both of you! You've really helped with an upcoming exam. This is my first time posting here, I will fill out my profile and hopefully I can help other people from here on in! Thanks again!

$$X_2^{1-\alpha}=\frac{1}{X_2^{\alpha -1}}$$
also $$X_2^{-\alpha}=\frac{1}{X_2^\alpha}$$
also use the property $$x^ay^a=(xy)^a$$
you get
$$\frac{\alpha}{1-\alpha}\frac{(\frac{X_1}{X_2})^{\alpha-1}}{(\frac{X_1}{X_2})^\alpha}$$
