Question

If x = b + c -2a , y = c + a -2b, z = a + b -2c then the value of x 2 + y 2 - z 2 + 2xy is ???

Answer 1

x+y+z=0 by putting there given value
hence x+y=-z

now
x 2 + y 2 - z 2 + 2xy =(x+y)^2-z^2= (-z)^2-z^2=z^2-z^2=0