There are 1 questions in this calculation: for each question, the 1 derivative of x is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ cos(nx)cos(nx)cos(nx) - cos(nx)\ with\ respect\ to\ x：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = cos^{3}(nx) - cos(nx)\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( cos^{3}(nx) - cos(nx)\right)}{dx}\\=&-3cos^{2}(nx)sin(nx)n - -sin(nx)n\\=&-3nsin(nx)cos^{2}(nx) + nsin(nx)\\ \end{split}\end{equation} \]

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