let's recall that the sum of all interior angles in a triangle is 180°.
an equi-lateral, equal sides, triangle has all sides that are equal.
sides that are equal will yield an equal opposite angle.
so if all sides are equal, all angles are equal, for a sum of 180°, that's only possible with 60°, 60° and 60° angles, and all of them are acute, none obtuse.
