Prove convergence of a series little with Direct comparison test

114 Views Asked by At

I have the following series

$$\sum_{k=1}^{\infty} \log\left(1+\frac{1}{k^2}\right)$$

This series should converge but when I apply the Direct comparison test it diverges

$$\left|\sum_{k=1}^{\infty} \log(1+\frac{1}{k^2})\right| \le \sum_{k=1}^{\infty} \log\left|1+\frac{1}{k^2}\right| \le \sum_{k=1}^{\infty} 1+\frac{1}{k^2} = \sum_{k=1}^{\infty} 1 + \sum_{k=1}^{\infty}\frac{1}{k^2}$$

so we know that $\sum_{k=1}^{\infty} \left(1+\frac{1}{k^2}\right) = \sum_{k=1}^{\infty} 1 + \sum_{k=1}^{\infty}\frac{1}{k^2}$ diverges because $\sum 1$ diverges, so the series should diverges.

what am I doing wrong?

Should it be in this way :

$$\left|\sum_{k=1}^{\infty} \log(1+\frac{1}{k^2})\right| \le \sum_{k=1}^{\infty} \log\left|1+\frac{1}{k^2}\right| \le \sum_{k=1}^{\infty} \frac{1}{k^2}$$

so it will converges because $\sum \frac{1}{k^2}$ converges ? if yes, why do we ignore $\sum 1$