4) All right angles are equal. 5) If two straight lines in a plane are crossed by a transversal, and sum the interior angle of the same side of the transversal is less than two right angles, then the two lines extended will intersect. According to Euclid, the rest of geometry could be deduced from these five postulates.

King lego lepinWhen parallel lines get crossed by another line (which is called a Transversal ), you can see that many angles are the same, as in this example: These angles can be made into pairs of angles which have special names. Click on each name to see it highlighted

G.3 The student will solve practical problems involving complementary, supplementary, and congruent angles that include vertical angles, angles formed when parallel lines are cut by a transversal, and angles in polygons. Objectives: Students will be able to: Measure and classify angles. Identify and use congruent angles and the bisector of an angle