Thursday 19 December 2013

SEQUENCE AND SERIES A6

Find the number of terms in the following geometric progression 5+10+20+40+ … + 1280

Solution

G1=5, Gn=1280, r=2.

Gn = G1rn-1;

1280 = 5 x 2n-1;

1280 = 5 x 2n-1;       (Divide by 5 on both sides)
   5         5

256 = 2n-1;

256 = 2n x 2-1;


256 = 2n x 1/2;

256  =  2n;  (Divide by 1/2 on both sides)
  1/2      

512 =  2n;     (512 = 2x2x2x2x2x2x2x2x2)

29 =  2n;

9 = n


There are 9 terms in a Geometrical Progression.

No comments:

Post a Comment