There are 1 questions in this calculation: for each question, the 1 derivative of x is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ 6xcos(7x) - 21{x}^{2}sin(7x)\ with\ respect\ to\ x：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = 6xcos(7x) - 21x^{2}sin(7x)\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( 6xcos(7x) - 21x^{2}sin(7x)\right)}{dx}\\=&6cos(7x) + 6x*-sin(7x)*7 - 21*2xsin(7x) - 21x^{2}cos(7x)*7\\=&6cos(7x) - 84xsin(7x) - 147x^{2}cos(7x)\\ \end{split}\end{equation} \]

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