[thisisclick]

$Df(x)=\frac{x^{2}Dsin(x^{3})-sin(x^{3})Dx^{2}}{x^{4}}=\frac{3x^{4}cosx^{3}-2xsinx^{3}}{x^{4}}$
=$2cosx^{3}-\frac{2sinx^{3}}{x^{3}}$

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