Line Segment is the portion of the line between two points A and B. A line segment has two end points. Ray is a line segment AB when extended in one direction.
An infinite number of lines can be drawn through a point. All lines are called concurrent lines. One and only one line can be drawn passing through two given points.
If a line can pass through three or more points, then these points are said to be collinear points, otherwise points are non-collinear.
Two lines are called parallel lines if both have no points in common or if the distance between the lines is same everywhere.
Angle is formed by two rays with a common initial point called vertex and measured in degrees.
- Acute angle: An angle whose measure is less than 90º.
- Right angle: An angle whose measure is 90º.
- Obtuse angle: An angle whose measure is more than 90º but less then 180º.
- Straight angle: An angle whose measure is 180º.
- Reflex angle: An angle whose measure is more than 180º and less than 360º.
Two lines or rays making a right angle with each other are called perpendicular lines.
Complementary angles: Two angles are complementary if the sum of their measures is 90º.
Supplementary angles: Two angles are supplementary if the sum of their measures is 180º.
Adjacent angles: Two angles having a common vertex, a common arm and non common arms on opposite sides of the common arm.
When a transversal intersects two parallel lines, then
- each pair of corresponding angles are equal.
- each pair of alternate angles are equal.
- each pair of interior angles on the same side of the transversal are supplementary.
- ∠2 = ∠6, ∠3 = ∠7
- ∠3 = ∠6 and ∠4 = ∠5
- ∠3 + ∠5 = 180º and ∠4 + ∠6 = 180º