Mì-chit-fûn-ho̍k

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Chú-yeu khói-ngiam

$\begin{array}{cc}{f}^{\prime }(3)& =\underset{h\to 0}{\lim }\frac{(3+h{)}^2-3^2}{h}\\ & =\underset{h\to 0}{\lim }\frac{9+6h+h^2-9}{h}\\ & =\underset{h\to 0}{\lim }\frac{6h+h^2}{h}\\ & =\underset{h\to 0}{\lim }(6+h)\\ & =6.\end{array}$