##### Definition3.1.1

An $$n\times n$$ matrix $$A$$ is called invertible if there is a matrix $$B$$ such that $$BA = I_n\text{,}$$ where $$I_n$$ is the $$n\times n$$ identity matrix. The matrix $$B$$ is called the inverse of $$A$$ and denoted $$A^{-1}\text{.}$$

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