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Calculating the derivative of a function of the form $f(x)=ax^3$ from first principles.

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Differentiate $f(x)=\\simplify{{a}*x^3}$ from first principles.

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For a function $f(x)$, its derivative is defined as \\[\\frac{df}{dx}=\\frac{f(x+h) - f(x)}{h} \\quad\\text{in the limit as $h$ tends to $0$.}\\]

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This is written \\[ \\frac{df}{dx}= \\lim_\\limits{h\\to 0}\\frac{f(x+h) - f(x)}{h}.\\]

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So, for the function $f(x)=\\simplify{{a}*x^3}$,

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\\begin{split}\\frac{df}{dx}&=\\lim_\\limits{h\\to 0} \\frac{f(x+h)-f(x)}{h}\\\\ &=\\lim_\\limits{h\\to 0} \\frac{[ \\simplify{{a}*(x+h)^3}] - [\\simplify{{a}*x^3}]}{h}\\\\ &=\\lim_\\limits{h\\to 0} \\frac{\\simplify{{a}*[x^3+3*x^2*h+3x*h^2+h^3]}-\\simplify{{a}*x^3}}{h}\\\\ &=\\lim_\\limits{h\\to 0}\\frac{\\simplify{{a}*x^3}+\\simplify{3{a}x^2h}+\\simplify{3{a}x*h^2}+\\simplify{{a}*h^3}-\\simplify{{a}*x^3}}{h}\\\\ &=\\lim_\\limits{h\\to 0} \\simplify{3{a}x^2}+\\simplify{3{a}*x*h}+\\simplify{{a}h^2}\\\\ &=\\simplify{3{a}x^2}\\end{split}

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x^3 coefficient

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$\\frac{df}{dx}= $[[0]]

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