Giao luu:
\(a=\left(\frac{x}{\left(x-y\right)^2}-\frac{y}{x^2-y^2}\right)=\left(\frac{x\left(x+y\right)-y\left(x-y\right)}{\left(x-y\right)^2\left(x+y\right)}\right)=\left(\frac{x^2+y^2}{\left(x-y\right)^2\left(x+y\right)}\right)\)
\(b=\frac{x^3-xy^2}{\left(x^2+y^2\right)}=\frac{x\left(x^2-y^2\right)}{x^2+y^2}=\frac{x\left(x-y\right)\left(x+y\right)}{x^2+y^2}\)
\(c=\frac{y}{x-y}\)
\(P=c-ab\)
Điều kiện tồn tại P: \(!x!-!y!\ne0\)
\(P=\frac{y}{x-y}-\frac{x}{x-y}=\frac{y-x}{x-y}=-\frac{x-y}{x-y}=-1\)