- #1
zigzagdoom
- 27
- 0
Hi Guys,
I am self teaching some basic analysis out of interest and I have a question on trying to prove a series diverges.
Question; Prove that (-1)^n (1+1/n) diverges.
My attempted approach was through contradiction:
Assume that (-1)^n (1+1/n) converges. Then for some ε>0, there exists an N such that for all n>N,
|(-1)^n (1+1/n) - L | < ε
Then I broke down into two cases; n is odd, or n is even
Suppose n is even, then we have | 1+1/n - L | < ε = 1 + 1/n < ε + L
Now suppose that n is odd, then we have | -1 - 1/n - L | < ε = -1 - 1/n < ε + L
Here is where I get stuck, I do not see where the contradiction is. Intuitively I know that the series jumps due to the (-1)^n and so alternately moves away from L, but I cannot show this.
If you guys could point me to where I am going wrong I would greatly appreciate it.
Thanks,
ZZD
I am self teaching some basic analysis out of interest and I have a question on trying to prove a series diverges.
Question; Prove that (-1)^n (1+1/n) diverges.
My attempted approach was through contradiction:
Assume that (-1)^n (1+1/n) converges. Then for some ε>0, there exists an N such that for all n>N,
|(-1)^n (1+1/n) - L | < ε
Then I broke down into two cases; n is odd, or n is even
Suppose n is even, then we have | 1+1/n - L | < ε = 1 + 1/n < ε + L
Now suppose that n is odd, then we have | -1 - 1/n - L | < ε = -1 - 1/n < ε + L
Here is where I get stuck, I do not see where the contradiction is. Intuitively I know that the series jumps due to the (-1)^n and so alternately moves away from L, but I cannot show this.
If you guys could point me to where I am going wrong I would greatly appreciate it.
Thanks,
ZZD