You can do it that way, but it's not necessary. Remember, and this applies no matter what the sign of a,b or c are. If I were doing the problem I would apply the exponent to every term in the parentheses of the numerator, then work on moving around negative exponents such that they can be expressed as positive ones. I think once you simplify the numerator and don't write it as 1/something, the rest of the problem will be fairly simple since everything is multiplied together.