There are 1 questions in this calculation: for each question, the 1 derivative of x is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ cos(x)*3 + cos(21x) + \frac{cos(441x)}{3}\ with\ respect\ to\ x：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = 3cos(x) + cos(21x) + \frac{1}{3}cos(441x)\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( 3cos(x) + cos(21x) + \frac{1}{3}cos(441x)\right)}{dx}\\=&3*-sin(x) + -sin(21x)*21 + \frac{1}{3}*-sin(441x)*441\\=&-3sin(x) - 21sin(21x) - 147sin(441x)\\ \end{split}\end{equation} \]

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