GEOMETRICAL PROGRESSION 2

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

Solution

G₁ = 3, r=2, n=7

S_n = G₁(rⁿ-1)/r-1

                

S₇ = 3(2⁷-1)/2-1

             

S₇ = 3(2⁷-1)

S₇ = 3(128-1)

S₇ = 3(127)

S₇ = 381

Hence the sum of the 1st eight terms is 381.

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

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