Find one positive and one negative angle coterminal with an angle of 9pi/6

Answer 1

To find a coterminal angle in radians add or subtract 2pi as many times as needed.

9pi/6 + 2pi = 9pi/6 + 12pi/6 = 21pi/6

9pi/6 - 2pi = 9pi/6 - 12pi/6 = -3pi/6