Consider a (possibly complex-valued) function [itex]F(z) = F(x,y)[/itex] of two variables. Can it make sense to talk about the(adsbygoogle = window.adsbygoogle || []).push({}); differential[itex]dF[/itex] of this function without it having aderivative[itex]dF/dz[/itex]? Or must [itex]F[/itex] be differentiable before we can even start talking about [itex]dF[/itex]?

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# Differential vs. Derivative of a multivariable function

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