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Question -

The sum of first three terms of a G.P. is 13/12, and their product is тАУ 1. Find the G.P.



Answer -

Let the three numbersbe a/r, a, ar

So, according to thequestion

a/r + a + ar = 13/12 тАжequation (1)

a/r ├Ч a ├Ч ar = -1 тАжequation (2)

From equation (2) weget,

a3┬а=-1

a = -1

From equation (1) weget,

(a + ar + ar2)/r= 13/12

12a + 12ar + 12ar2┬а=13r тАж equation (3)

Substituting a = тАУ 1in equation (3) we get

12( тАУ 1) + 12( тАУ 1)r +12( тАУ 1)r2┬а= 13r

12r2┬а+25r + 12 = 0

12r2┬а+16r + 9r + 12 = 0тАж equation (4)

4r (3r + 4) + 3(3r +4) = 0

r = -3/4┬аor r =-4/3

Now the equation willbe

-1/(-3/4), -1, -1├Ч-3/4or -1/(-4/3), -1, -1├Ч-4/3

4/3, -1, ┬╛ or ┬╛, -1,4/3

тИ┤┬аThe threenumbers are┬а4/3, -1, ┬╛ or ┬╛, -1, 4/3

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