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Questions about the properties of vector spaces and linear transformations, including linear systems in general.
27
votes
Should the formula for the inverse of a 2x2 matrix be obvious?
I remember the inverse by looking at the corresponding linear fractional transformation. It sends $\frac{-d}{c}$ to $\infty$ and $\infty$ to $\frac{a}{c}$, so the inverse had better reverse this; it f …