Question

What is the common denominator?

3 2
- + -
1 a-1
-------
4 3
- - -
1 a+1

Answer 1

If your denominator on the top is (a-1) and your denominator on the bottom is (a+1) then your common denominator is (a-1)(a+1) which by the way is (a^2-1)

Answer 2

Thank you very much. It helped me not only on that problem but others as well. :)

Answer 3

"........but others as well."

Good! That is the whole idea :) You are very welcome.