There are 1 questions in this calculation: for each question, the 2 derivative of x is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ second\ derivative\ of\ function\ cos(7x)cos(7x)\ with\ respect\ to\ x：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = cos^{2}(7x)\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( cos^{2}(7x)\right)}{dx}\\=&-2cos(7x)sin(7x)*7\\=&-14sin(7x)cos(7x)\\\\ &\color{blue}{The\ second\ derivative\ of\ function:} \\&\frac{d\left( -14sin(7x)cos(7x)\right)}{dx}\\=&-14cos(7x)*7cos(7x) - 14sin(7x)*-sin(7x)*7\\=&-98cos^{2}(7x) + 98sin^{2}(7x)\\ \end{split}\end{equation} \]

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