Sunday, 29 April 2018

G.P 1


The sum of the 1st five terms of a geometrical progression is 484. If the common ratio is 3 find the 4th 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

G4 = G1r4-1

G4= G1r 3

G4 = 4 x (3)3

     = 4 x 27

     = 81


Hence the 4th term is 81.

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


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

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