The inverse of A = \pmatrix{ a & b \cr c & d} is
A^{-1} = \displaystyle \frac{1}{ad-bc} \pmatrix{ d & -b \cr -c & a }

Remember that in general AB \ne BA

Remember that in general AB \ne BA

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## Glossary

### union

The union of two sets A and B is the set containing all the elements of A and B.