Cho x^2 + y^2 + z^2 = 10. Tính P = (xy + yz + zx)^2 + (x^2 - yz)^2 + (y^2 - xz^2) + (z^2 - zy)^2
$P=x^2y^2+y^2z^2+z^2x^2+2xy^2z+2yz^2x+2zx^2y+x^4-2x^2yz+y^2z^2+y^4-2y^2xz+x^2z^2+z^4-2z^2xy+z^2y^2\\=x^4+y^4+z^2+2x^2y^2+2y^2z^2+2z^2x^2\\=(x^2+y^2+z^2)^2\\=10^2\\=100$