A line has direction cosines $\frac{2}{7}$, $\frac{3}{7}$ and $n$, with $n > 0$. What is $n$?

Explanation

1. 01

   $l^{2} + m^{2} + n^{2} = 1$: $n^{2} = 1 - \frac{4}{49} - \frac{9}{49} = \frac{36}{49}$.

2. 02

   $n = \frac{6}{7}$.