# Lines in three dimensional space

There are also **lines** in three-dimensional space. However, their equation does not look like the equation of a linear function.

Instead of a slope, you have a **direction vector** in space. Lines have a definite position (as opposed to vectors).

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### Remember

A line is uniquely defined by a point and a direction vector.

## Parametric equation of a line

The parametric equation of a line is:

$\text{g: } \vec{x} = \vec{a} + r \cdot \vec{m}$

$\text{g: } \vec{x} = \vec{OA} + r \cdot \vec{AB}$

The equation consists of

- a
**support vector**: This is the position vector of any point on the line. - the
**direction vector**that determines the direction of the line.

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### Info

The factor $r$ in front of the direction vector is about scalar multiplication.
This means that the direction vector can be extended arbitrarily (by $r$), since the line on both sides goes to infinity.