GEOMETRICAL PROGRESSION 1

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

Solution

G₁ = 2, r=3, n=6

S_n = G₁(rⁿ-1)/ r-1

               

S₇ = 2(3⁶-1) /3-1

             

S₇ = ¹2(3⁶-1)

        2₁

S₇ = (3⁶-1)

S₇ = 729 - 1

S₇ = 728

Hence the sum of the 1st seven terms is 728.

TRY THIS……………………………

Find the sum of the 1st seven terms of the geometrical progression 2+8+32+…….