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.