How to check if function is differentiable at a point

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The discussion focuses on determining the differentiability of the complex function \( w = z |z| \) at the point (0,0). The function is expressed in terms of its real and imaginary components, \( u = x\sqrt{x^2+y^2} \) and \( v = y\sqrt{x^2+y^2} \). By applying the Cauchy-Riemann equations, the results indicate that the function is differentiable at (0,0), despite concerns about the limit behavior at that point. The limit of the expressions as \( (x,y) \) approaches (0,0) is confirmed to be well-defined and equal to zero.

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Fabio010
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The question is to check where the following complex function is differentiable.

w=z \left| z\right|



w=\sqrt{x^2+y^2} (x+i y)


u = x\sqrt{x^2+y^2}
v = y\sqrt{x^2+y^2}
Using the Cauchy Riemann equations

\frac{\partial }{\partial x}u=\frac{\partial }{\partial y}v
\frac{\partial }{\partial y}u=-\frac{\partial }{\partial x}v


my results:

\frac{x^2}{\sqrt{x^2+y^2}}=\frac{y^2}{\sqrt{x^2+y^2}}
\frac{x y}{\sqrt{x^2+y^2}}=0


solutions says that it's differentiable at (0,0). But doesn't it blow at (0,0)?
 
Last edited:
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What do you mean with "blow"?
The limit of those expressions for x,y -> 0 is well-defined and zero.
 

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