You can
put this solution on YOUR website!5pi/3 does correspond to a main angle. And you can do it with only the unit circle.
First locate 5pi/3 on the unit circle. The x-coordinate of that point (you determine this using the special right triangle) is the cosine of that angle, and the y-coordinate is the sine of that angle. Since tangent of an angle is defined as the sine over the cosine, you can find tan(5pi/3).