SUM OF A G.P - 1

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

Solution

G₁ = 3, r=2, n=6

S_n = G₁(rⁿ-1)/r-1

               

S₇ = 3(2⁶-1)/2-1

            

S₇ = 3(2⁶-1)

S₇ = 3(64-1)

S₇ = 3(63)

S₇ = 189

Hence the sum of the 1st eight terms is 189.

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

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