There are 1 questions in this calculation: for each question, the 1 derivative of x is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ 6cos(7x) - 84xsin(7x) - 147x*2cos(7x)\ with\ respect\ to\ x：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = 6cos(7x) - 84xsin(7x) - 294xcos(7x)\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( 6cos(7x) - 84xsin(7x) - 294xcos(7x)\right)}{dx}\\=&6*-sin(7x)*7 - 84sin(7x) - 84xcos(7x)*7 - 294cos(7x) - 294x*-sin(7x)*7\\=&-126sin(7x) - 588xcos(7x) - 294cos(7x) + 2058xsin(7x)\\ \end{split}\end{equation} \]

Your problem has not been solved here? Please take a look at the  hot problems ！