Simplify: 1a−1b1a2−1b2\frac{\frac{1}{a} - \frac{1}{b}}{\frac{1}{a^2} - \frac{1}{b^2}}a21−b21a1−b1 for a,b≠0a, b \neq 0a,b=0, a≠ba \neq ba=b.
ababab
aba+b\frac{ab}{a+b}a+bab
a+ba + ba+b
aba−b\frac{ab}{a-b}a−bab