Find the extremal values of f(x,y,z) = x + y + z subject to the constraints x² + y² = 2 and x + z = 1.
a) f(x,y,z) = 2 - z
b) f(x,y,z) = 2 + z
c) f(x,y,z) = 3 - z
d) f(x,y,z) = 3 + z