Question

ab-1 – a-1b
a-1 + b-1

Answer 1

(ab⁻¹ - a⁻¹b)/(a⁻¹ + b⁻¹)
= (a/b - b/a) / (1/a + 1/b)
= ((a² - b²)/ab) / ((a + b)/ab)
= (a² - b²)/(a + b)
= (a + b)(a - b) / (a + b)
= a - b