There are 1 questions in this calculation: for each question, the 2 derivative of t is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ second\ derivative\ of\ function\ 9cos(6t) - 7sin(6t) + 2tsin(6t)\ with\ respect\ to\ t：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( 9cos(6t) - 7sin(6t) + 2tsin(6t)\right)}{dt}\\=&9*-sin(6t)*6 - 7cos(6t)*6 + 2sin(6t) + 2tcos(6t)*6\\=&-52sin(6t) - 42cos(6t) + 12tcos(6t)\\\\ &\color{blue}{The\ second\ derivative\ of\ function:} \\&\frac{d\left( -52sin(6t) - 42cos(6t) + 12tcos(6t)\right)}{dt}\\=&-52cos(6t)*6 - 42*-sin(6t)*6 + 12cos(6t) + 12t*-sin(6t)*6\\=&-300cos(6t) + 252sin(6t) - 72tsin(6t)\\ \end{split}\end{equation} \]

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