11. What is the inverse of the matrix

A	B.	C.
D.	E.

Solution The answer is D.

There are various ways of doing this problem. You could apply the usual algorithm for computing the inverse of a 3 x 3 matrix. Start with the 3 x 6 augmented matrix

Then subtract the second row from the first to get

Finally, subtract the third row from the second to obtain

The inverse is the matrix of the last three columns in this last matrix.