If
\[
\frac{x^{2}+1}{(x^{4}+5x^{2}+6)(x^{6}+x^{4})}
=
\frac{A}{x^{4}}+\frac{B}{x^{2}}+\frac{C}{x^{2}+2}+\frac{D}{x^{2}+3},
\]
then \(A-B=\):
Show Hint
When repeated factors like \(x^4\) appear in partial fractions, coefficients of
\(\frac1{x^4}\) and \(\frac1{x^2}\) are most easily obtained by substituting \(x=0\) and comparing derivatives.