If
\[
\frac{x+3}{(1-x)^2(1+x^2)}
=
\frac{A}{(1-x)}
+
\frac{B}{(1-x)^2}
+
\frac{Cx+D}{2(1+x^2)},
\]
then \(B^2+C^2+D^2=\)
Show Hint
For repeated linear factors in partial fractions,
\[
\boxed{\text{Substitute the repeated root first to obtain the highest power coefficient.}}
\]
The remaining constants can then be found using differentiation or coefficient comparison.