If w=f(z)=u(x,y)+iv(x,y), f(z) analytic, defines a transformation from the variables x, y to the variables u, v, show that the Jacobian of the transformation (see Chapter 10, Section 13) is ∂(u,v)/∂(x,y)=∣f′(z)∣2. Hint: To simplify the determinant, use the Cauchy-Riemann equations and the equations (Section 2) used in obtaining them.