Exercise 8, § 7

Show that, if $m$ is an integer $> 0$, then $\sum_{n \geq 1, n \neq m} \frac{1}{m^2 - n^2} = - \frac{3}{4m^2}$ (express the rational fraction $\frac{1}{m^2 - x^2}$ as a sum of partial fractions).