There are 1 questions in this calculation: for each question, the 1 derivative of L is calculated.
    Note that variables are case sensitive.
\[ \begin{equation}\begin{split}[1/1]Find\ the\ first\ derivative\ of\ function\ -{L}^{3} + 48L + 9{L}^{2}\ with\ respect\ to\ L：\\\end{split}\end{equation} \]\[ \begin{equation}\begin{split}\\Solution:&\\ &Primitive\ function\ = -L^{3} + 48L + 9L^{2}\\&\color{blue}{The\ first\ derivative\ function：}\\&\frac{d\left( -L^{3} + 48L + 9L^{2}\right)}{dL}\\=&-3L^{2} + 48 + 9*2L\\=&-3L^{2} + 18L + 48\\ \end{split}\end{equation} \]

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