Unit 2A - Proofs/Justifications

Day 1 & 2 - Angle Relationships :

(Key: Bigger bullets are for memorization, smaller ones are helpful notes that don’t need memorization)

• Perpendicular lines create right angles

• A right angle measures 90 degrees

  • Complementary angles are two angles whose sum is 90 degrees

  • Supplementary angles are two angles whose sum is 180 degrees

• Linear pairs are supplementary

• The whole angle is equal to the sum of its parts

• The sum of angles that form a line is 180 degrees

• The sum of all the adjacent angles with the same vertex is 360 degrees

• Vertical angles are congruent

Day 3 - Transversals & Angle Relationships with Parallel Lines:

• If 2 parallel lines are cut by a transversal, then corresponding angles are congruent

• If 2 parallel lines are cut by a transversal, then alternate interior angles are congruent

• If 2 parallel lines are cut by a transversal, then consecutive interior angles are supplementary

• If 2 parallel lines are cut by a transversal, then alternate exterior angles are congruent

Day 4 - Proving Lines are Parallel:

• If corresponding angles are congruent, then the lines are parallel

• If alternate interior angles are congruent, then the lines are parallel

• If consecutive angles are supplementary, then the lines are parallel

• If alternate exterior angles are congruent, then the lines are parallel

• If 2 lines are perpendicular to the same line, then they are parallel to each other

• If a line is perpendicular to one of two parallel lines, it is perpendicular to the other

  • Vertical angles do not create parallel lines

  • Linear pairs do not create parallel lines