To classify the angle of a triangle (acute, obtuse, or right), you can use slope formula to see if the slopes are perpendicular. If so, it is a right triangle. The distance formula can be applied to figure out whether the triangle is isosceles, equilateral, or scalene. if the triangle is isosceles, then two of the sides will be the same length and one side will be of a different length. If the triangle is equilateral, then all sides will be of the same length. If the triangle is scalene, then all side will be of different lengths.