Chapter 9.3, Problem 88PE

For Exercises 87-92, use matrices $A,B$ , and $C$ to prove the given properties. Assume that the elements within $A,B$ , and $C$ are real numbers.

$A=\left[\begin{array}{cc}{a}_1& a_2\\ a_3& a_4\end{array}\right]B=\left[\begin{array}{cc}{b}_1& b_2\\ b_3& b_4\end{array}\right]C=\left[\begin{array}{cc}{c}_1& c_2\\ c_3& c_4\end{array}\right]$

Associate property of matrix addition $A+\left(B+C\right)=\left(A+B\right)+C$