It may help to see all of the symmetries of an equilateral triangle, and then writing down the subsequent rotations or reflections required to get back to the original image. For the equilateral triangle, its symmetry group is $$ \\{e, r, r^2, s, rs, r^2s\\} $$ where $r$ is a counterclockwise rotation of 120$^\circ$ and $s$ is a reflection across an axis of symmetry (there are other ways to define its dihedral group; this is just one of them). Visually, , which makes sense, because $$ (r^2s)(sr) = r^2s^2r = r^2r = e $$ since $r^3 = e$ and $s^2 = e$. So try to think about the inverses visually, then write them down and check if it makes sense algebraically.