If 5^-p = 4^-q = 20^r, show that : 1/p + 1/q + 1/r = 0 .

Given, ⇒ 5 -p = 4 -q = 20 r = k (let) ⇒ 5 -p = k ⇒ 5 = .......(1) ⇒ 4 -q = k ⇒ 4 = ......(2) ⇒ 20 r = k ⇒ 20 = ............(3) We know that, ⇒ 5 × 4 = 20 From equations (1), (2) and (3), we get : Hence, proved that .