Simplify: 1a−1b1a+1b\dfrac{\dfrac{1}{a} - \dfrac{1}{b}}{\dfrac{1}{a} + \dfrac{1}{b}}a1+b1a1−b1 (assume a,b≠0a, b \neq 0a,b=0, a≠ba \neq ba=b).
b−ab+a\dfrac{b - a}{b + a}b+ab−a
a−ba+b\dfrac{a - b}{a + b}a+ba−b
ab\dfrac{a}{b}ba
ba\dfrac{b}{a}ab