Answer:
P1 (6, 2/3 π)
P2 (6, 10/3 π)
P3 (6, 14/3 π)
Explanation:
To find the other three points you take into account that if you sum 2π to one coordinate you have the same point.
Hence, by adding 2π to -4π/3, and again other two times:
hence, the other two points are
P1 (6, 2/3 π)
P2 (6, 10/3 π)
P3 (6, 14/3 π)