Unit A: Geometry

Chapter 1: Polygons

Summary

Types of Triangles

• Triangles can be classified according to angles or side lengths.

• The three type of triangles classified according to angle measures are right, acute, and obtuse.
• Right triangles have one angle equal to 90°.
• Acute triangles have all angles less than 90°.
• Obtuse triangles have one angle more than 90°.

• The three types of triangles classified according to side lengths are equilateral, isosceles, and scalene.
• Equilateral triangles have all three equal sides and all three equal angles.
• Isosceles triangles have two equal sides and two equal angles.
• Scalene triangles have no equal sides and no equal angles.

Sum of the Angles in a Triangle

• The sum of the angles in a triangle is 180°.

• $\angle A+\angle B+\angle C=180°$