There are 1 questions in this calculation: for each question, the 2 derivative of t is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ second\ derivative\ of\ function\ 5cos(3t) + 2sin(3t) + 6tsin(3t)\ with\ respect\ to\ t：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( 5cos(3t) + 2sin(3t) + 6tsin(3t)\right)}{dt}\\=&5*-sin(3t)*3 + 2cos(3t)*3 + 6sin(3t) + 6tcos(3t)*3\\=&-9sin(3t) + 6cos(3t) + 18tcos(3t)\\\\ &\color{blue}{The\ second\ derivative\ of\ function:} \\&\frac{d\left( -9sin(3t) + 6cos(3t) + 18tcos(3t)\right)}{dt}\\=&-9cos(3t)*3 + 6*-sin(3t)*3 + 18cos(3t) + 18t*-sin(3t)*3\\=&-9cos(3t) - 18sin(3t) - 54tsin(3t)\\ \end{split}\end{equation} \]

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