Question
Mathematics Question on Series
Let an=i(n+1)2, where i=−1 and n=1,2,3..... . Then the value of a1+a3+a5+...+a25 is
A
13
B
13+i
C
13−i
D
12
Answer
13
Explanation
Solution
Given, an=i(n+1)2
∴ a1=i22=1,a2=i32=i, a3=i42=1,a4=i52=i, a5=i62=1,..........
∴ For all odd values of n, we get the value of an is 1.
∴ a1+a3+a5+....+a25
=131+1+1+......+1
=13