If the nth term of a GP 5,-5/2,5/4,-5/8,..... is 51024, then the value of n is
11
10
9
4
Explanation for the correct answer.
Given: GP 5,-5/2,5/4,-5/8,..... and nth term of GP is 51024
Let abe the first term and r be the common ratio of the given GP
a=5r=a2a1=-525=-12
Nth term of GP is an=arn-1
⇒arn-1=51024⇒5-12n-1=51024⇒-12n-1=-1210⇒n-1=10⇒n=11
Hence, option (a) is correct.
If the sum of n terms of an A.P. is 2n2+5n, then its nth term is