# How do you express as a partial fraction 1/(s^2 +1)^2?

We can try to find a partial fraction decomposition by finding $A , B , C , \text{ and } D$ so that:
$\frac{A s + B}{{s}^{2} + 1} + \frac{C s + D}{{s}^{2} + 1} ^ 2$ (as the method tells us to do),
But we get $A = 0$, $B = 0$, $C = 0$ and $D = 1$, which is what we started with.