((x^-2)^-2))/((x^-2-y^-2)^-2) = .....

$$(x^{-2})^{-2}\div (x^{-2}-y^{-2})^{-2}\\\\
=(x^{-2*-2})\times (x^{-2}-y^{-2})^{+2}\\\\
=(x^{4})\times (\frac{1}{x^2}-\frac{1}{y^2})^{+2}\\\\
=(x^{4})\times (\frac{y^2-x^2}{x^2y^2})^2\\\\
=(x^{4})\times \frac{(y^2-x^2)^2}{x^4y^4}\\\\
=\frac{(y^2-x^2)^2}{y^4}\\\\
=\frac{y^4-2x^2y^2+x^4}{y^2}\\\\

.$$