Answer:
1 / √3
Explanation:
210° is in Quadrant III, and is 30° past 180°. Thus, the opp side is negative and could be represented by -1. The adj side is also negative and could be represented by -√3.
Thus, the tangent of 210° is opp / adj = -1 / (-√3), or 1 / √3.
This could also be written as √3 / 3.