algebra
posted by Sandra .
Reduce each rational expression to lowest terms. Assume that the
variables represent only numbers for which the denominators are
nonzero.
a^2b^2/ab

I assume you mean (a^2b^2)/(ab)
a^2  b^2 factors to (ab)(a+b) by the difference of two squares.
You now have (ab)(a+b)/(ab). The (ab) cancel out, leaving you with (a+b)