= Plane mirror
{wiki}
A <plane mirror> has a flat reflecting <surface>. The <law of reflection> sends incident unit direction $\mathbf d$ to $\mathbf d-2(\mathbf d\cdot\mathbf n)\mathbf n$, where $\mathbf n$ is its <unit normal>. It forms a <virtual image> of an object the same perpendicular distance behind the reflecting plane as the object is in front. Two successive <plane mirrors> whose planes meet at <angle> $\gamma$ rotate the ray geometry through $2\gamma$ about their intersection.
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