To classifiy Triangles is by Length & Angle. Length triangles are like Isosceles, Equilateral, & Scalene. Isosceles Triangles has only 2 sides the same. Equilaterals Triangles have ALL sides the same. Scalene Triangle has NONE sides the same. Now Angle Triangles are on Obtuse, Acute, & Right Angles. Obtuse Triangles have 1 obtuse angle. Acute Trianglehas all 3 acute angles. Right Triangle have only 1 Right Angle.