Path of Light
Sketching with Math and Quasi Physics
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Reflection
$${r=i-\frac{2i\cdot n}{\left\|n\right\|^2}n}$$
$${i}$$: vector of the ray to the surface, $${n}$$: normal of the surface, $${r}$$: vector of the reflected ray
Parabola
Parallel rays coming into a parabolic mirror converge at a single focal point