1. Geometry
4.1 Triangle and Angles

2. Acute Triangle
A triangle where all three angles are acute angles.
Obtuse Triangle
A triangle where one of the three angles is an obtuse angle.
Right Triangle
A triangle where one of the three angles is a right angle.

3. Equiangular Triangle
An acute triangle where all three angles are congruent.
Scalene Triangle
A triangle with no two sides being congruent.
Isosceles Triangle
A triangle with at least two sides being congruent.

4. Equilateral Triangle
A triangle with all three sides congruent.

5. Exterior Angle Theorem
The measure of an exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles.
Triangle Sum Theorem
The sum of the measures of the angles of a triangle is 180.