SUM OF A GP 1

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

solution

G₁ = 2, r=3, n=7

S_n = G₁(rⁿ-1)/r-1

               

S₇ = 2(3⁷-1)/3-1

             

S₇ = ¹2(3⁷-1)/2₁

              

S₇ = (3⁷-1)

S₇ = 2187 - 1

S₇ = 2186

Hence the sum of the 1st seven terms is 2186.

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Find the sum of the 1st six terms of the geometrical progression 7+14+28+56+…..