Which of the following is true for the function f(x)=∑n=1∞cos(nx)n2f(x) = \sum_{n=1}^\infty \frac{\cos(nx)}{n^2}f(x)=∑n=1∞n2cos(nx)?
It is nowhere continuous.
It is continuous but not differentiable everywhere.
It is differentiable everywhere.
It is only defined at x=0x=0x=0.