Direction Cosines and the Equation of a Line
Describing the direction of a line in 3D space, and writing its equation.
Direction Cosines
The cosines of the angles a line makes with the $x$, $y$, and $z$ axes, satisfying $l^2 + m^2 + n^2 = 1$.
Equation of a Line
The vector equation of a line through a point $\vec{a}$ and parallel to $\vec{b}$:
$$\vec{r} = \vec{a} + \lambda \vec{b}$$Lesson 26 of 32