There are 1 questions in this calculation: for each question, the 1 derivative of x is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ -cos(a) + mcos(x) + ncos(x - a) + p\ with\ respect\ to\ x：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( -cos(a) + mcos(x) + ncos(x - a) + p\right)}{dx}\\=&--sin(a)*0 + m*-sin(x) + n*-sin(x - a)(1 + 0) + 0\\=& - msin(x) - nsin(x - a)\\ \end{split}\end{equation} \]

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