Basics of Geometry




Session: 
Point: It is an exact location. It is a fine dot which has neither length nor breadth nor thickness but has position i.e., it has no magnitude.
Line segment: The straight path joining two points A and B is called a line segment AB . It has and points and a definite length.
Ray: A line segment which can be extended in only one direction is called a ray.
Intersecting lines: Two lines having a common point are called intersecting lines. The common point is known as the point of intersection.
Concurrent lines: If two or more lines intersect at the same point, then they are known as concurrent lines.
Angles: When two straight lines meet at a point they form an angle.
Right angle: An angle whose measure is 90^{o} is called a right angle.
Acute angle: An angle whose measure is less then one right angle (i.e., less than 90^{o}), is called an acute angle.
Obtuse angle: An angle whose measure is more than one right angle and less than two right angles
(i.e., less than 180^{o} and more than 90^{o}) is called an obtuse angle.
Reflex angle: An angle whose measure is more than 180^{o} and less than 360^{o} is called a reflex angle.
Complementary angles: If the sum of the two angles is one right angle (i.e., 90^{o}), they are called complementary angles. Therefore, the complement of an angle θ is equal to 90° − θ
Supplementary angles: Two angles are said to be supplementary, if the sum of their measures is 180^{o}.
Example: Angles measuring 120^{o} and 60^{o} are supplementary angles. Two supplementary angles are the supplement of each other. Therefore, the supplement of an angle θ is equal to 180° − θ.