NIMCET 2018 Question Paper with solutions

Question : 42 of 120

Marks: +1, -0

Sum to infinity of a geometric progression is twice the sum of the first two terms. Then, what are the possible values of the common ratio?

Solution:

According to question ,
G.M = 2 (a+ar)
⇒

a/{1-r}

= 2 (a + ar)
⇒

1/{1-r}

= 2 (1 + r)
⇒ (1 + r) (1 - r) =

1/2

⇒

1-r^2

1/2

r^2

1/2

⇒ r = ±

1/√2

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