Math - Rotation Matrix

In this lecture we looked at how to build a rotation matrix to help us rotate our objects in 2D.

For your challenge we were trying to rotate a box by 30 degrees.
This box had it’s vertices at points; (0, 0) || (2, 0) || (2, 2) || (0, 2)

Did you manage to find where each point ends up after applying the rotation matrix?
Post your answers below and remember to use the spoiler tags.

I feel like I did something wrong, but I got:

a = (0,0)
c = (1.23, 2.73)
d = (1, 3^1/2)

I got D by flipping the coordinates for B, but then I switched the sign of x to get (-1, 3^1.2) because x clearly has be be negative.

Did I miss something? I went back to review how to get the dot product, but maybe I miscalculated somewhere?