SEQUENCE AND SERIES A4

Find the sum of the 1st eight terms of the geometrical progression 3+6+12+24+…….

Solution

G₁ = 3, r=2, n=8

S_n = G₁(rⁿ-1)/r-1

               

S₈ = 3(2⁸-1)/ 2-1

            

S₈ = 3(2⁸-1)

S₈ = 3(256-1)

S₈ = 3(255)

S₈ = 765

Hence the sum of the 1st eight terms is 765.