Which of these series is an alternating series?
∑n=1∞1n\sum_{n=1}^{\infty} \frac{1}{n}∑n=1∞n1
∑n=1∞(−1)n1n2\sum_{n=1}^{\infty} (-1)^n \frac{1}{n^2}∑n=1∞(−1)nn21
∑n=1∞n2\sum_{n=1}^{\infty} n^2∑n=1∞n2
∑n=1∞(0.5)n\sum_{n=1}^{\infty} (0.5)^n∑n=1∞(0.5)n