Saturday 26 November 2016

GEOMETRIC PROGRESSION 4


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

solution

G1 = 2, r=3, n=8

Sn = G1(rn-1)/r-1
               
S8 = 2(38-1)/3-1
             
S8 = 12(38-1)/21
              
S8 = (38-1)

S7 = 6561 – 1               [Since  38  =6561]

S7 = 6560

Hence the sum of the 1st seven terms is 6560.

TRY THIS………………



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

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