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Types of anglesThere are many different types of angles. We will define them in this lesson.
Acute angle: An angle whose measure is less than 90 degrees. The following is an acute angle. ![]() Right angle: An angle whose measure is 90 degrees. The following is a right angle. ![]() Obtuse angle: An angle whose measure is bigger than 90 degrees but less than 180 degrees. Thus, it is between 90 degrees and 180 degrees. The following is an obtuse angle. ![]() Straight angle An angle whose measure is 180 degrees.Thus, a straight angle look like a straight line. The following is a straight angle. ![]() Reflex angle: An angle whose measure is bigger than 180 degrees but less than 360 degrees.The following is a reflex angle. ![]() Adjacent angles: Angle with a common vertex and one common side. <1 and <2, are adjacent angles. ![]() Complementary angles: Two angles whose measures add to 90 degrees. Angle 1 and angle 2 are complementary angles because together they form a right angle. Note that angle 1 and angle 2 do not have to be adjacent to be complementary as long as they add up to 90 degrees ![]() Supplementary angles: Two angles whose measures add to 180 degrees. The following are supplementary angles. ![]() Vertical angles: Angles that have a common vertex and whose sides are formed by the same lines. The following(angle 1 and angle 2) are vertical angles. ![]() When two parallel lines are crossed by a third line(Transversal), 8 angles are formed. Take a look at the following figure ![]() Angles 3,4,5,8 are interior angles Angles 1,2,6,7 are exterior angles Alternate interior angles: Pairs of interior angles on opposite sides of the transversal. For instance, angle 3 and angle 5 are alternate interior angles. Angle 4 and angle 8 are also alternate interior angles. Alternate exterior angles: Pairs of exterior angles on opposite sides of the transversal. Angle 2 and angle 7 are alternate exterior angles. Corresponding angles: Pairs of angles that are in similar positions. Angle 3 and angle 2 are corresponding angles. Angle 5 and angle 7 are corresponding angles Here we go! Study the types of angles carefully. This is where any serious study of geometry begin. You may want to check also Central angles. |
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Complementary and supplementary angles|
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