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Given a vector (*a*,*b*,*c*) in three-space, the **direction cosines**
of this vector are

Here the **direction angles** , , are the
angles that the vector makes with the positive *x*-, *y*- and
*z*-axes, respectively. In formulas, it is usually the direction
cosines that occur, rather than the direction angles. We have

*Silvio Levy
Wed Oct 4 16:41:25 PDT 1995*

This document is excerpted from the 30th Edition of the *CRC Standard Mathematical Tables and Formulas* (CRC Press). Unauthorized duplication is forbidden.