SUM OF A GP 1

Find the sum of the 1st ten terms of the geometrical progression 2+6+18+54+…….

solution

G₁ = 2, r=3, n=10

S_n = G₁(rⁿ-1)/r-1

               

S₁₀ = 2(3¹⁰-1)/3-1            

S₁₀ = ¹2(3¹⁰-1)/2₁

               

S₁₀ = (3¹⁰-1)

S₁₀ = 59049 - 1

S₁₀ = 59048

Hence the sum of the 1st seven terms is 19682.

TRY THIS………………

Find the sum of the 1st eight terms of the geometrical progression 3+9+27+81+…..