GEOM. PROGRESSION 3

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

Solution

G₁ = 3, r=2, n=9

S_n = G₁(rⁿ-1)/r-1

               

S₉ = 3(2⁹-1)/2-1

             

S₉ = 3(2⁹-1)/1

              

S₉ = 3(2⁹-1)

S₉ = 3(512-1)

S₉ = 3(511)

S₉ = 1533

Hence the sum of the 1st nine terms is 1533.

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

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