Chapter 5 Notes
Angles and Similarity
5.1 Classifying Angles
▪ Two angles whose sum is 90 degrees are called complementary.
▪ Two angles whose sum is 180 degrees are called supplementary.
▪ Two angles are called congruent if they have the same angle
measure.
▪ Two angles are called vertical angles if they are opposite of each
other and the angles are formed by two intersecting lines. Vertical
angles are always congruent (the same angle measure).
5.2 Angles and Sides of Triangles
▪ The sum of the angle measures of a triangle is always 180 degrees.
▪ An isosceles triangle has at least two congruent sides (those two
sides are the same length).
▪ An equilateral triangle has three congruent sides.
▪ An equilateral triangle is also equiangular (all three angles are the
same!).
5.4 Using Similar Triangles
▪ If two triangles are similar, then they will have the same angle
measures or two triangles are similar only if they have the same
angle measures.
▪ Use similar figures to find a missing measure when it’s difficult to
measure directly (If necessary, flip or rotate your figures before
setting up your proportion).
5.5 Parallel Lines and Transversals
▪ Lines on the same plane that never intersect are parallel lines.
▪ A transversal is a line that intersects two or more parallel lines.
▪ Corresponding angles lie on the same side of the transversal and are
in the same corresponding position. They are always congruent.
▪ Interior angles lie inside of the two parallel lines. Alternate interior
angles are on opposite sides of the transversal and are congruent.
▪ Exterior angles lie outside of the two parallel lines. Alternate exterior
angles are on opposite sides of the transversal and are congruent.
▪ Vertical angles are opposite each other and are congruent.