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Lines and Angles

In this topic, we learn about different parts of a line and the classification of lines. We also learn to classify angles.

Topic: Parts of a Line

  • A straight path that goes forever in both directions is a line

  • A straight path with 2 endpoints is a line segment

  • A straight path that goes on forever in one direction from an endpoint is a ray

Topic: Classification of Lines

  • Lines can be classified by their different relationships to other lines within a plane

  • Lines that cross at a point are called intersecting lines

  • Lines in a plane that never intersect and are the same distance apart at every point are called parallel lines

  • Lines that intersect to form four right angles are called perpendicular lines

Topic: Classification of Angles

  • The square angles formed by two lines are right angles. A right angle measures 90°

  • A straight angle is an angle on a straight line. It measures exactly 180°

  • An acute angle measures less than 90° (less than a right angle)

  • An obtuse angle measures more than 90° and less than 180°(more than a right angle, but less than a straight angle)

Topic: Degree Measure and Fraction of a Turn

  • An angle that is 90o is 1/4 turn on a circle. It is also a right angle

  • An angle that is 180o is 1/2 turn on a circle. A 180o angle is a straight angle

  • An angle that is 270o is 3/4 turn on a circle

  • An angle that is 360o is a full turn on a circle
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