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In geometry, a normal is an object such as a line or vector that is perpendicular to a given object. For example, in the two-dimensional case, the normal line to a curve at a given point is the line perpendicular to the tangent line to the curve at the point.

### Normal to surfaces in 3D space

### Hypersurfaces in ''n''-dimensional space

### Varieties defined by implicit equations in ''n''-dimensional space

### Uses

### Normal in geometric optics