A quick question regarding one of the practice problems.

cos(x)=-0.1.

We are looking for an angle for which the x coordinate is -0.1. Therefore, quadrant II and III.

Take the inverse: x = 1.671.

The solutions according to the answers is 1.67+ 2pi . n and -1.67 + 2pi . n.

I get the first solution. My issue is with the second solution, where I get:(2pi-1.67 = 4.6132) + 2pi . n which is what I get on Mathway as well.

Note: solutions are in radians.

I think there is a gap in my knowledge, so any advice would be appreciated.