There are 1 questions in this calculation: for each question, the 1 derivative of u is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ \frac{kff}{(u - f)}\ with\ respect\ to\ u：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = \frac{kf^{2}}{(u - f)}\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( \frac{kf^{2}}{(u - f)}\right)}{du}\\=&(\frac{-(1 + 0)}{(u - f)^{2}})kf^{2} + 0\\=&\frac{-kf^{2}}{(u - f)^{2}}\\ \end{split}\end{equation} \]

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