x² + y² = zz = 2 - √(x² + y²) ==> √(x² + y²) = 2 - z ==> x² + y² = (2 - z)² = 4 - 4z + z²z = 4 - 4z + z² ==> z² - 5z + 4 = 0 ==> (z - 4)(z...