Triangles can be classified by their angle measures and side lengths. For triangles only, equiangular and equilateral have the same implications: all sides and angles are congruent. Isosceles triangles have at least two congruent sides and two congruent angles. Right triangles contain an angle whose measure is 90 degrees. All the angles in an acute triangle are less than 90 degrees. Knowing the different types of triangles is important when solving proofs.