Cho x^2 + y^2 = 2yz

Cho x^2 + y^2 = 2yz
        y^2 + z^2 = 2zx
        z^2 + x^2 = 2xy
Tính A = (x + y - 2z)^5 + (x+z-2y)^5 + (y+z-2y)^5