 In the equilateral triangle case, since all sides are equal, any side can be called the base.Whether an isosceles triangle is acute, right or obtuse depends only on the angle at its apex.In Euclidean geometry, the base angles can not be obtuse (greater than 90°) or right (equal to 90°) because their measures would sum to at least 180°, the total of all angles in any Euclidean triangle.