Flashcards

The direction cosines are found by dividing the direction ratios by the magnitude of the vector they represent: $l= \pm \frac{a}{\sqrt{a^{2}+b^{2}+c^{2}}}, m= \pm \frac{b}{\sqrt{a^{2}+b^{2}+c^{2}}}, n= \pm \frac{c}{\sqrt{a^{2}+b^{2}+c^{2}}}$ where the signs for $l, m,$ and $n$ are taken to be the same.