An angle of measure [tex]\frac{4\pi }{3}[/tex] intersects the unit circle at point ([tex]-1/2,- \frac{\sqrt{3} }{2}[/tex]). What is the exact value of tan([tex]\frac{4\pi }{3}[/tex])?
a. -1/2
b. [tex]\sqrt{3[/tex]
c. [tex]\frac{\sqrt{3} }{3}[/tex]
d. [tex]-\frac{\sqrt{3} }{2}[/tex]