Reduce each rational expression to lowest terms. Assume that the
variables represent only numbers for which the denominators are
nonzero.
a^2-b^2/a-b
I assume you mean (a^2-b^2)/(a-b)
a^2 - b^2 factors to (a-b)(a+b) by the difference of two squares.
You now have (a-b)(a+b)/(a-b). The (a-b) cancel out, leaving you with (a+b)