Thanks for the link to the original question. This is:
I suspect that the = sign should really be an sign. In other words, the two sides of the equation have to be identically equal. So you need to work out what the indices of and are on the LHS (in terms of and ), and equate them to the indices on the RHS. That's where your two equations will come from.
So, let me start you off. I'll begin by bringing the two terms in the denominators of the LHS into the numerator, by changing the signs of their indices:
So when we equate the indices on each side, we get:
Can you continue from here?