Wednesday 7 December 2016

SUM OF A GP 2


The sum of the 1st five terms of a geometrical progression is 484. If the common ratio is 3 find the 2nd term.

solution

S5 = 484, G1 = ?, r=3, n=5, A2=?

 We use the summation formula to find the 1st term.

Sn = G1(rn-1)/r-1
               
S5 = G1(r5-1)/r-1
                
484= G1(35-1)/3-1
                
484= G1(243-1)
                  2

2 x 484= G1(242)
                  
968= 242 G1

4 968   =  G1
  242

G1 = 4

Now we solve for the 2nd term.

Gn = G1rn-1

G2 = G1r2-1

G2 = G1r

G2 = 4 x 3

     = 12


Hence the 2nd term is 12.


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



The sum of the 1st five terms of a geometrical progression is 484. If the common ratio is 3 find the 1st term.  

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