Write the Word or Phrase That Best Completes Each Statement $L=\left[\begin{array}{ccc}1 & m & n \\ p & q & r\end{array}\right], X=\left[\begin{array}{lll}x & y & z \\ u & v & w\end{array}\right]$

Essay

Write the word or phrase that best completes each statement or answers the question
-Using the matrices $L=\left[\begin{array}{ccc}1 & m & n \\ p & q & r\end{array}\right], X=\left[\begin{array}{lll}x & y & z \\ u & v & w\end{array}\right]$ , and $A=\left[\begin{array}{lll}a & b & c \\ d & e & f\end{array}\right]$ , verify that $\mathrm{L}+(\mathrm{X}+\mathrm{A})=(\mathrm{L}+\mathrm{X})+\mathrm{A}$ .