Упростите выражения
(y^-2-x^-2)^-1*(x^-1-y^-1)

(y^-2-x^-2)^-1*(x^-1-y^-1) =
= 1/(1/y^2-1/x^2) * (1/x-1/y) =
= 1/(1/y-1/x)(1/y+1/x) * (1/x-1/y) =
= 1/(1/y-1/x)(1/y+1/x) * [-(1/y+1/x)] =
= -1/(1/y-1/x)
Как-то так...