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.
Two lines are intersecting lines if they meet each other at a common point.
Example, l1 and l2 are intersecting lines in the diagram
A Pair of lines are Parallel if they never intersect.
Example, L1, L2, and L3 are parallel lines in the diagram.
A Transversal line cuts two or more lines at distinct points.
Example, Line L3 is the transversal line in the diagram.
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An Angle is formed when two lines intersect each other. We represent an angle by the symbol ∠.
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:
When the measurement of the angle is between 0 degrees and 90 degrees.
When the measurement of the angle is exactly 90 degree.
If there is a right angle between two lines, then the two lines are said to be perpendicular to each other.
When the measurement of the angle is between 90 degrees and 180 degrees.
A straight line has an angle of 180 degrees.
When the measurement of the angle is between 180 degrees and 360 degrees.
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Introduction to Lines & Angles
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Let us now discuss the angles formed when two lines are intersected by a third line i.e. a transversal line.
- Interior angles are the ones that are present inside the region between two lines.
Exterior angles are the ones that are not present inside this region.
For example:
Two angles are said to be corresponding angles if they lie on the same side of the transversal line such that:
- One angle is an interior angle,
- Another is an exterior angle
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:
(∠1, ∠7) and (∠4, ∠6) are alternate exterior angles.
Note: If a transversal line intersects two parallel lines, then the corresponding angles, alternate interior angles, and alternate exterior angles are equal.
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. How are lines and angles related in geometry? |
3. What are the different types of angles formed by intersecting lines? |
4. What is the significance of parallel and perpendicular lines in angles? |
5. How can I calculate the measure of an angle formed by two intersecting lines? |
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