I think the best method for you is to write the answers out and see. Plug in n=1 for the first term, n=2 for the second, etc.,= 1/3 + 1/5 + 1/7 + ... = 1/1 + 1/3 + 1/5 + ... = 1/1 + 2/3 + 3/5 + ... = 1/3 + 2/5 + 3/7 + ... Now you know which one it is. Edwin
1. A(subscript)n=1/(2n+1) 2. A(subscript)n=1/(2n-1) <<<===<<< This one. 3. A(subscript)n=n/(2n-1) 4. A(subscript)n=n/(2n+1)