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If the nth term of an GP is an = (-1)n-1 5n+1 then find the common ratio of the GP is?
1. - 5
2. 5
3. 25
4. - 25

1 Answer

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Best answer
Correct Answer - Option 1 : - 5

CONCEPT:

If a is the first term and r is the common ratio of a GP. Then the nth term of an GP is given by: an = arn-1 where r = a2 / a1

CONCEPT:

Given: The nth term of an GP is an = (-1)n-1 5n+1 

So, first lets find out the first term and the second term of the given GP.

⇒ a1 = 25 and a2 = - 125

As we know that, if a is the first term and r is the common ratio of a GP. Then the nth term of a GP is given by: an = arn-1 where r = a2 / a1

⇒ r = - 125 / 25 = - 5

Hence, the correct option is 1.

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