Friday, 20 December 2013

SEQUENCE AND SERIES A7

The sum of the 1st five terms of a geometrical progression is 341. If the common ratio is 4 find the 1st term.

Solution

S5 = 341 G1 = ?, r=4, n=5

Sn = G1(rn-1)/  r-1
             

S5 = G1(r5-1)/ r-1
              

341= G1(45-1)/4-1
               

341= G1(1024-1)
                  3

3 x 341= G1(1023)
                  
1023= 1023 G1

1023=  G1
1023

G1 = 1


Hence the 1st term is 1.
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