Triangle Sum / Similar Triangles

The Triangle Sum Theorem states that the sum of the interior angles of a triangle is always 180 degrees.

Same side interior angles are pairs of angles that lie on the same side of a transversal and between two parallel lines.

Alternate interior angles are pairs of angles that lie on opposite sides of a transversal and between two parallel lines.

Vertical angles are the angles opposite each other when two lines intersect. They are always congruent.

Angle B measures 120 degrees because supplementary angles sum to 180 degrees.

Corresponding angles are equal when two parallel lines are cut by a transversal.

The other angle measures 60 degrees because complementary angles sum to 90 degrees.

Angle EDB measures 15 degrees.

Alternate interior angles, alternate exterior angles, corresponding angles, and same side interior angles are formed.

Angle 2 measures 55 degrees.