Chapter Three:  
Parallel and Perpendicular Lines

Geometry   Notes

Chapter  3

Section  3.1
Section  3.2
Section  3.3
Section  3.4
Section  3.5
Section  3.6
Section  3.7

Geometry Contents

Take notes on the following topics.

Section 3-3  Parallel Lines and the Triangle Angle-Sum Theorem

Vocabulary

Acute triangle (p. 133) An acute triangle has three acute angles.

Right triangle (p. 133) A right triangle contains one right angle. The side opposite the right angle is the hypotenuse and the other two sides are the legs.

Obtuse triangle (p. 133) An obtuse triangle has one obtuse angle.

Equiangular triangle  (p. 133) An equiangular triangle is a triangle whose angles are all congruent. 

Equilateral triangle  (p. 133) An equilateral triangle is a triangle whose sides are all congruent. 

Isosceles triangle (p. 133) An isosceles triangle is a triangle that has at least two congruent sides. If there are two congruent sides, they are called legs. The vertex angle is between them. The third side is called the base and the other two angles are called the base angles.

Scalene triangle (p. 133) A scalene triangle has no sides congruent.

Exterior angle of a polygon (p. 133) An exterior angle of a polygon is an angle formed by a side and an extension of an adjacent side.

Remote interior angle (p. 133) Remote interior angles are the two nonadjacent interior angles corresponding to each exterior angle of a triangle.

 

Theorem 3-7  Triangle Angle-Sum Theorem

The sum of the measures of the angles of a triangle is 180.

Theorem 3-8   Triangle Exterior Angle Theorem

The measure of the exterior angle of a triangle is equal to the sum of the measures of the two remote interior angles.