F(x)=cos3x/x производная

[latex]f'(x)=( \frac{cos3x}{x} )'= \frac{(cos3x)'*x-x'*cos3x}{ x^{2} } = \frac{-sin3x*(3x)'*x-cos3x}{ x^{2} } =[/latex] [latex]=- \frac{x*sin3x+cos3x}{ x^{2} } [/latex]