Points, lines, and angles.

• A point is a dimensionless location in space.
• We label a point with a capitol letter.
• Points are zero dimension objects.
• A line is a collection of points.
• Labeled as two capital letters.
• A ray starts at one end point and goes on forever in one direction.
• Lines are one dimensional objects.
• Two lines which do not intersect are called parallel lines
• When two lines intersect, they meet at a point.
  • This forms an angle.
  • The intersection point is called the vertex.
  • angle ABC, angle CBA, angle B are all the same.
  • The two rays are called sides.
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• Angles are measured in degrees (0 to 360) or radians (0 to 2π)
  • An angle with a measure of 90° is a right angle
  • An angle with a Maurie of 180° is a straight angle
  • An angle with a measure < 90° is an acute angle
  • An angle with a measure > 90° is an obtuse angle
  • 
• If two angles share an common side, they are adjacent angles
  • If the sum of two adjacent angles is 90° the angles are complementary
  • If the sum of two adjacent angles is 180° the angles are supplementary
  • 
• If two lines intersect, vertical angles are formed.
  • Vertical angles are equal. Why?
  • 
  • angle 1 and angle 3 are are vertical angles.
  • angle 2 and angle 4 are vertical angles.
• If two parallel lines are cut by a transversal
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  • Alternate interior angles are equal.
  • Angle 3 and angle 6 are alternate interior angles.
  • Angle 4 and angle 5 are alternate interior angles.
  • Alternate exterior angles are equal.
  • Angle 1 and angle 8 are alternate exterior angles.
  • Angle 2 and angle 7 are alternate exterior angles.
  • Corresponding angles are equal.
  • Angle 1 and angle 5 are corresponding angles.
  • Angle 2 and angle 6 are corresponding angles.
  • Angle 3 and angle 7 are corresponding angles.
  • Angle 4 and angle 8 are corresponding angles.

Homework