A line does not have any endpoints. It has an infinite length.
A line segment is a segment of a line, or in other words, we can say that a line segment is a line with two endpoints.
For example, The diagram shows a line L and one segment of this line is AB.
In a plane, there can be many lines or line segments.
And, these lines can be divided into a few types based on the relative positioning of a line with another line.
Intersecting Lines
Two lines are intersecting lines if they meet each other at a common point.
For example, L_{1} and L_{2} are intersecting lines in the below diagram
A pair of lines are parallel if they never intersect.
For example, L_{1}, L_{2}, and L_{3} are parallel lines in the below diagram.
A transversal line cuts two or more lines at distinct points.
For example, Line L_{3} is the transversal line in the below diagram.
An angle is formed when two lines intersect each other. We represent an angle by the symbol ∠.
An angle involves two legs and one common vertex at which two lines meet.
For example, ∠AOD is formed when lines AB and CD intersect with each other.
Also, ∠AOD is formed between the leg AO and OD, so we include A, O, and D while naming the angle.
The angle is measured in degrees.
An angle can measure from zero (0) degrees to 360 degrees. Based on the measurement of an angle, they are divided into four types:
Acute Angle
When the measurement of the angle is between 0 degrees and 90 degrees.
Right Angle
When the measurement of the angle is exactly 90 degree.
Obtuse Angle
When the measurement of the angle is between 90 degrees and 180 degrees.
A straight line has an angle of 180 degrees.
Reflex Angle
Vertically Opposite Angles
When two lines intersect each other, then 4 angles are formed.
Let us now discuss the angles formed when two lines are intersected by a third line i.e. a transversal line.
When a transversal line intersects two lines, then eight angles are formed as shown.
Now, there are several special pairs of angles that are obtained from this diagram.
For example: If you notice (∠1, ∠3), (∠2, ∠4), (∠5, ∠7), and (∠6, ∠8) are all vertically opposite angles.
Similarly, we get several other types of angles. Let us discuss them.
Interior and Exterior Angles
Interior angles are the ones that are present inside the region between two lines.
For example:
Two angles are said to be corresponding angles if they lie on the same side of the transversal line such that:
For example:
(∠4, ∠8), (∠3, ∠7), (∠1, ∠5), and (∠2, ∠6) are 4 pairs of corresponding angles
Two interior angles, present on the opposite side of a transversal line, are called alternate interior angles.
For example:
(∠2, ∠8) and (∠3, ∠5) are alternate interior angles.
Two exterior angles that are present on the opposite side of the transversal line are called alternate exterior angles.
For example:
Note: If a transversal line intersects two parallel lines, then the corresponding angles, alternate interior angles, and alternate exterior angles are equal. So, we have discussed all the type of angles. Let us now learn about a few properties of angles.
Sum of angles on one side of a straight line
The sum of all the angles on one side of a straight line is always 180 degrees.
For example, The sum of ∠1, ∠2, and ∠3 is 180 degrees.
Sum of angles around a point
The sum of all the angles around a point is always 360 degrees.
For example, Sum of angles (∠1, ∠2, and ∠3) around point O is 360 degrees.
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1. What is a line in geometry? 
2. What are the different types of lines? 
3. How can you determine if lines are parallel or perpendicular? 
4. Can lines have endpoints? 
5. What is the importance of lines in geometry? 

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