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• (a) $\displaystyle \sum _ {n = 1} ^ {\infty} \left (\frac{n} {n+1} \right) ^ {n^2}$ (b) $\displaystyle \sum _ {n = 1} ^ {\infty} \frac{\cos \left (n \pi \right)} {n+2}$
• (c) $\displaystyle \sum _ {n = 1} ^ {\infty} n \sin ^2 \left (\frac{1} {n} \right)$