SUM OF A GP 1

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)/1

              

S₈ = 3(2⁸-1)

S₈ = 3(256-1)

S₈ = 3(255)

S₈ = 765

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

TRY THIS.........................

Find the sum of the 1st nine terms of the geometrical progression 5+10+20+40+…….