Given that a is a geometric sequence and a2 20 and a3 100

Given that a is a geometric sequence and a2 = 20 and a3 = 100

what is the common ratio r?

Solution

let common ratio of this geometric sequence be \'r\'

and first term be a₁

hence a₂ = a₁r = -20

and a₃ = a₁r² = 100

a₃/a₂ = r = -5

hence common ratio is -5