Simple trig equation confusion

Hi, I'm a little confused over the following question:

3sin2x-1=0 on the interval XE[0,2pi]

Working it out, I got:

2x=sin-1(1/3)

Two solutions as: ~0.17 rad and ~1.4 rad

However, the answers show that there are four solutions: 0.17, 1.4, 3.31, 4.54

Most of the previous questions have only had 2 solutions and the only question I've encountered with more included cubes.

Could anyone help me figure out where the other two solutions came from and what I should be looking for in future questions of the same nature?

Thanks!