Tuesday 17 December 2013

SEQUENCE AND SERIES A2

Find the number of terms in the following geometric progression 2+6+18+54+ ….. + 1458

Solution

G1=2, Gn=1458, r=3.

Gn = G1rn-1;

1458 = 2 x 3n-1;

1458 = 2 x 3n-1;
 2          2

729 = 3n-1;

729 = 3n x 3-1;


729 = 3n x 1/3; (dividing by 1/3 on both sides)


729  =  3n;
  1/3      

2187 =  3n;

2187 =  3n;     (2187 = 3x3x3x3x3x3x3)

37 =  3n;

7 = n


Hence There are 7 terms in a Geometrical Progression.



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