• A line-segment has two end points.
  • A ray has only one end point (its vertex).
  • A line has no end points on either side.
  • An angle is formed when two lines (or rays or line-segments) meet.
  • Pairs of Angles Condition
    Two complementary angles Measures add up to 90°
    Two supplementary angles Measures add up to 180°
    Two adjacent angles Have a common vertex and a common arm but no common interior.
    Linear pair   Adjacent and supplementary



  • When two lines a and b intersect; the point of their meet is called the point of intersection.
  • When 2 lines do not meet at any point however far we extend them, we call these lines as parallel lines.
  • Line: A line is perfectly straight and extends forever in both directions.
  • Line segment: A line segment is the part of a line between two points.
  • Ray: A ray is part of a line that starts at one point and extends forever in one direction.
  • Intersecting lines: Two or more lines that have one point in common.
  • Transversal: A line intersects two or more lines that lie in the same plane in distinct points.
  • Parallel lines: Two lines on a plane that never meet. They are always the same distance apart.
  • Complementary Angles: Two angles that add to 90°.
  • Supplementary Angles: Two angles that add to 180°.
  • Adjacent Angles: Two angles have a common vertex and a common arm but no common interior points.
  • Linear pairs: A pair of adjacent angles whose non-common sides are opposite rays.
  • Vertically Opposite Angles: Two angles formed by intersection of two lines that have common arm.
  • Angles made by Transversal: When two lines are intersecting by a transversal, eight angles are formed.
  • Transversal of Parallel Lines: If two parallel lines are intersected by a transversal, then each pair of:
    • Corresponding angles are congruent.
    • Alternate interior angles are congruent.
    • Alternate exterior angles are congruent.
  • If the transversal is perpendicular to the parallel lines, all of the angles formed are congruent to 90° angles.
  • Sum of any 2 sides of triangle is greater than its third side.
  • In right angled triangle, hypotenuse is the longest side.
  • Sum of angles of triangle is 180 degree.
  • A, B, C are collinear if AB + BC = AC.

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