If `x+y+z=0` , then `x^2+x y+y^2` equals `y^2+y z+z^2` (b) `y^2-y z+z^2` (c) `z^2-z x+x^2` (d) `z^2+z x+x^2`

What should be added to x y+y z+z x to get x y-y z-z x ? -2x y-2y z-2z x (b) -3x y-y z-z x -3x y-3y z-3z x (d) 2x y+2y z+2z x

If x + y = 2z then (x)/(x-z) +(z)/(y-z) = ?

If x+y+z=0 then what is the value of (1)/(x^(2)+y^(2)-z^(2)) +(1)/(y^(2)+z^(2)-x^(2)) +(1)/(z^(2)+x^(2)-y^(2)) ?