Źródło TeX:

f^{\prime }(x)=(-\frac{4}{5\sqrt{x^{5}} })^{\prime }= -4\cdot \frac{1}{5}(x^{-\frac{5}{2}})^{\prime }=-\frac{4}{5} \cdot (-\frac{5}{2})x^{-\frac{7}{2}} =2x^{-\frac{7}{2}}=\frac{2}{\sqrt{x^{7}}}