NETMaths

Is this true?

The Cauchy–Riemann equations at a point imply complex differentiability there

No — it is false.

The counterexample

for z ≠ 0, f(0) = 0

CR hold at 0, but the difference quotient along z = t(1+i) differs from the one along the real axis.

The kind of mistake this is

Hypothesis dropped

A theorem applied without checking one of its preconditions.

Drill statements like this

Others that fail the same way

From Analytic FunctionsCauchy–Riemann equations, harmonic functions

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