If $x,y,z$ are real numbers satisfying$x/(y+z) +y/(z+x) +z/(x+y) =1$ then $x^2/(y+z) +y^2/(z+x)+z^2/(x+y)=$ I have tried it a few times but I am not making any progress. Please help.

$$\dfrac{x^2}{y+z}+\dfrac{y^2}{z+x}+\dfrac{z^2}{x+y}$$
$$=\dfrac{x^2}{y+z}+x+\dfrac{y^2}{z+x}+y+\dfrac{z^2}{x+y}+z-(x+y+z)$$
$$=(x+y+z)\left(\dfrac x{y+z}+\cdots\right)-(x+y+z)$$
$$=?$$
