# The sum of an inf

Let the first term Of G.P. be a, and common ratio be r.

On cubing each term will become,

a3, a3r3, ….

This sum

a=57(1-r) put this in equation 2 we get

19(1-2r+r2)=1+r+r2

19r2-r2-38r-r+19-1=0

18r2-39r+18=0

6r2-13r+6=0

(2r-3)(3r-2)=0

r= 2/3, 3/2

But -1<r<1

r=2/3

Substitute this value of r in equation 1 we get

Thus the first term of G.P. is 19, and the common ratio is 2/3

G.P=19,

19,

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