Angle Relationships in Triangles and Transversals

An angle is formed when two rays, lines, or line segments meet.

I can measure angles using a protractor. The unit given is degrees.

A full circle shows 360°. A half circle shows 180°. A quarter circle shows 90°.

The sum of the measures of the new angles is equal to the measure of the original angle.

Answers will vary. Encourage students to hypothesize.

Supplementary angles have measures that sum to 180°. If I know one angle in a supplementary angle pair, I can subtract it from 180 to find the measure of the missing angle.

The measures of the angles in a triangle add to 180°.

When two lines intersect, vertical angles are opposite each other. Vertical angles are congruent, so they have equal measure.

A transversal is a line that intersects a pair of parallel lines.

Corresponding angles are in the same position on both intersections; they are congruent. Interior angles are both on the inside of the parallel lines; they are supplementary. Exterior angles are both on the outside of the parallel lines; they are supplementary. Alternate angles are across from each other on different lines; alternate exterior and alternate interior angles are congruent.