Line
A line has neither initial nor terminal points with indefinite length.
The pairs of lines are nothing but the two lines, which may be intersects or parallel or perpendicular as shown below:
Angle
The region between two infinitely long lines pointing a certain direction (ray) from a common point (or vertex) is termed as an angle. That is, the amount of turn is measured by an angle, which can be commonly measured by an instrument called “protractor”. The symbol for an angle is “ ∠ ”.
The angles are classified into several types based on the angle measures:
- Acute angle:Angle that is less than 90 °
- Right angle:Angle that is exactly equal to 90 °
- Obtuse angle:Angle that is greater than 90 ° and less than 180 °
- Straight angle:Angle that is exactly equal to 180 °
- Obtuse angle:Angle that is greater than 180 ° and less than 360 °
- Complete (Full) angle:Angle that is exactly equal to 360 °
If the lines or line segments intersects, then the angles are formed. The relations between angles are characterized by the pairs of angles are:
- Complementary angles – Sum of the two angles is right angle
- Supplementary angles – – Sum of the two angles is straight angle
- Vertical opposite angles – The angles opposite each other when two lines cross is known as vertical opposite angles. . They are always equal.
- Linear pairs of angles – Alternate interior angles, alternate exterior angles and corresponding angles
Linear pair axiom
Two adjacent angles are said to be form a linear pair of angles, if their non-common arms are two opposite rays. Linear pair axiom theorems are if a ray stands on a line, then the sum of two adjacent angles so formed is 180 degree.
For more in depth knowledge refer to lines and angles class 9 ncert solutions pdf.
