Answer
(a) identity
(b) A, A
(c) inverse
Work Step by Step
The identity matrix $I_{n}$ is the $n\times n$ matrix whose main diagonal entries are all 1 and whose other entries are all $0$.
If $A$ is an $m\times n$ matrix, then
$AI_{n}=A$ and $I_{m}A=A$
If $A$ is an $n\times n$ matrix, then the inverse of $A$ is the $n\times n$ matrix $A^{-1}$ with the following properties:
$A^{-1}A=I_{n}$ and $AA^{-1}=I_{n}$
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Fill the blanks with :
(a) identity
(b) A, A
(c) inverse
