Exercise · ZW-CAUCHY-RIEMANN-EQUATIONS-009 · ★★★ Advanced
If \(f=u+iv\) satisfies the Cauchy-Riemann equations at a point, what can be asserted?
Choose one option.
Show answer
- C. Nothing more unless \(u\) and \(v\) are differentiable there
Explanation
The equations are necessary for complex differentiability, but they suffice only if \(u\) and \(v\) are also (real) differentiable at the point.
Review the concept: Cauchy-Riemann equations
The two equalities between the partial derivatives of the real part \(u\) and the imaginary part \(v\) of a function \(f=u+iv\) that is differentiable at a point.
\[u_x=v_y,\qquad u_y=-v_x\]
More practice problems: cauchy-riemann equations
- ZW-CAUCHY-RIEMANN-EQUATIONS-001 For f(z)=z^2 we have u=x^2-y^2 and v=2xy. What is u_x?
- ZW-CAUCHY-RIEMANN-EQUATIONS-002 Which is the correct pair of Cauchy-Riemann equations?
- ZW-CAUCHY-RIEMANN-EQUATIONS-003 For f(z)=e^z, with u=e^xcos y and v=e^xsin y, what is v_y?
- ZW-CAUCHY-RIEMANN-EQUATIONS-004 For f(z)=bar z, with u=x and v=-y, at which points does u_x=v_y hold?
- ZW-CAUCHY-RIEMANN-EQUATIONS-005 For f(z)=|z|^2, with u=x^2+y^2 and v=0, at which points do the Cauchy-Riemann equations hold?
- ZW-CAUCHY-RIEMANN-EQUATIONS-006 If f=u+iv is differentiable at z, then f'(z)=u_x+iv_x. Compute f'(1+i) for f(z)=z^2.
- ZW-CAUCHY-RIEMANN-EQUATIONS-007 Let u=x^2-y^2. Which v, with v(0,0)=0, makes u and v satisfy Cauchy-Riemann?
- ZW-CAUCHY-RIEMANN-EQUATIONS-008 Let u=e^xcos y. Which v satisfies Cauchy-Riemann together with u?
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