The consecutive terms of a geometric progression

Three consecutive terms of a geometric progression

If e, f and g are 3 consecutive terms of GP, then

g f = f e

Example 

If p+20,p4,p20   are three consecutive terms of a geometric progression, find the value of p.

Solution

p20 p4 = p4 p+20
(P+20)(p20)=(p4)(p4) 
p 2 400= p 2 8p+16 
8p=416 
p=52