## Calculus (3rd Edition)

$$e=\langle \cos \frac{4 \pi }{7}, \sin \frac{4 \pi }{7}\rangle.$$
A unit vector $e$ making an angle of $\frac{4 \pi }{7}$ with the x-axis is given by $$e=\langle \cos \frac{4 \pi }{7}, \sin \frac{4 \pi }{7}\rangle.$$