Chapter 6.3, Problem 1E

(a) The matrix $I=\left[\begin{array}{rr}\hfill 1& \hfill 0\\ \hfill 0& \hfill 1\end{array}\right]$ is called an _____ matrix.
(b) If A is a $2\times 2$ matrix, then $A\times I=$ _____ and $I\times A=$ _____.
(c) If A and B are $2\times 2$ matrices with $AB=I$ , then B is the _____ of A.