The Exterior Angle Inequality Theorem

Theorem-The measure of an exterior angle of a triangle is greater than the measure of either remote interior angle.

Indentifying Parallel Lines

Theorem-If two lines are cut by a transversal such that the alternate interior angles are congruent, then the lines are parallel.

Theorem-If two lines are cut by a transversal such that the alternate exterior angles are congruent, then the lines are parallel.

Theorem- If two lines are cut by a transversal such that the corresponding angles are congruent, then the lines are parallel.

Theorem-If two lines are cut by a transversal such that the two interior angles on the same side are supplementary, then the lines are parallel.

Theorem-If two lines are cut by a transversal such that the two exterior angles on the same side are supplementary, then the lines are parallel.

Theorem- If two coplanar lines are perpendicular to a third line, they are parallel.