First find the inverse of :

To do that:

1.  Find the value of its determinant, 

2. Swap the upper left and lower right elements of ,
getting 

3. Then change the signs of the upper right and lower left elements,
getting 

4. Divide every element by the value of the determinant of the 
original matrix which we found to be 13 in step 1, getting
. This is the inverse of
the original matrix.

Left-multiply both sides of the given matrix equation:



by this inverse:

 

Use the associative principle to move the parentheses around
the first two matrices on the left:

 

Do the matrix multiplication:



Simplify:



Simplify some more:



Simplify some more:



Multiply the matrices on the left:



Simplify:



Edwin