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[tex]\lim_{\Delta z\to 0}\frac{f(z+h)-f(z)}{\Delta z}[/tex]

[tex]f(z) = |z| = \sqrt{x^2+y^2}[/tex]

[tex]\Delta z = \Delta x + i\Delta y[/tex]

[tex]\lim_{\Delta x\to 0}\frac{\sqrt{(x+\Delta x)^2+(y+\Delta y)^2}- \sqrt{x^2+y^2}}{\Delta x}[/tex]

Is that correct? Or do I just have the delta x with the x? Or is there a x + delta x and y + delta y?

Thanks.