$$\frac{x+y}{(x+y)^{2}-z^{2}}+\frac{y-z}{x^{2}-(y-z)^{2}}-\frac{z+x}{(z+x)^{2}-y^{2}}$$
((x+y)*(-y+x+z)+(y-z)*(x+y+z)-(z+x)*(x+y-z))/((x+y+z)*(x+y-z)*(-y+x+z))