Cauchy-Riemann Equations and Complex Derivatives: A Homework Problem

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SUMMARY

The discussion centers on the application of the Cauchy-Riemann equations to the function f(z) = x^3 + i(1-y)^3. It is established that the derivative f'(z) can be expressed as f'(z) = u_x + iv_x = 3x^2 only at the point z = i. The Cauchy-Riemann equations, u_x = v_y and u_y = -v_x, are crucial for determining the legitimacy of the complex derivative, which requires that the conditions x^2 = -(1-y)^2 be satisfied.

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Homework Statement



Show that when f(z)=x^3+i(1-y)^3, it is legitimate to write:

f'(z)=u_x+iv_x=3x^2
only when z=i

Homework Equations



Cauchy riemann equations:

u_x=v_y , u_y=-v_x
f'(z)=u_x+i*v_y

The Attempt at a Solution


u=x^3
v=(1-y)^3
u_x=3*x^2
v_y=-3*(1-y)^2
x^2=-(1-y)^2 =

u_y=0
-v_x=0

f'(z)=3*x^2+i(0)= 3*x^2

I don't understand why z=i => z=o+i*1? is relevant to show that f'(z)=3*x^2
 
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f'(z) only has a complex derivative if it satisfies the Cauchy-Riemann equations. You have correctly found that means x^2=-(1-y)^2. How many values of x and y satisfy that?
 

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