Well you're correct in saying that it's because it's a regular hexagon and so if one triangle is an equilateral, then all of them are. If you want a mathematical way to prove it, then if the point around N is 360° because it's around a point, then you can divide 360 by 6 (6 triangles) to get 60°. That is the angle of ENX, and therefore it is an equilateral triangle because all angles in an equilateral triangle are 60°. I hope this helps!
