\textbf{Problem 2.48} Consider matrix M =
      $$\begin{pmatrix}
        1 & a & b \\
        0 & 1 & c \\
        0 & 0 & 1
      \end{pmatrix}$$ \\
      where $a, b, c \in \mathbb{R}$ Because
      $$\begin{pmatrix}
        1 & a & b \\
        0 & 1 & c \\
        0 & 0 & 1
      \end{pmatrix}
      \begin{pmatrix}
        1 & a' & b' \\
        0 & 1 & c' \\
        0 & 0 & 1
      \end{pmatrix}
      =
      \begin{pmatrix}
        1 & a + a' & b' + ac' + b \\
        0 & 1 & c' + c \\
        0 & 0 & 1
      \end{pmatrix}$$