Why not just go ahead and make the substitution?
First, separate the function, with terms including on the left side of the equation and terms without an component on the right. Then, take out a common factor of from the left. Write everything remaining on the left as one fraction, and everything on the right as one fraction. Then divide/multiply through as necessary so that you're left with something of the form to simplify. If you need further help, please try this method yourself and show me how far you can get.
I then advised that you split the terms so that terms involving an were on the left and terms without were on the right, and take a common factor of
My next piece of advice was to rewrite everything on each side over a common denominator.
Now we can just multiply through by , as my previous response implied, to get:
I've done the majority for you now - see if you can finish.