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Geometry has always been an exciting and vital topic of mathematics. The Lines and Angles chapter of Class 9 Mathematics introduces you to essential geometry chapters. We know that angles are formed when any two lines intersect or meet. MCQ on Lines and Angles Class 9 chapter focuses mainly on the properties of angles formed in two conditions:

When two lines intersect each other.

When a line crosses two or more parallel lines.

In some more detail, let us look up NCERT Class 9 Lines and Angles MCQs in this chapter. We know that the base of the chapter must be crystal clear to understand each topic in detail and in the best way possible. We have to be clear with basic terms and definitions and the difference between them, such as line segment, ray, collinear points, and non-collinear points. Thus, we cover the basics of lines.

Angles are just like the heart and soul of geometry. An angle is born when two rays originate from a common point or two or more lines intersect. In this chapter, we come across five types of angles. They are:

Acute Angle

An angle is acute when it measures less than 90 degrees but is greater than 0. In short, the acute angle is an angle between 0 and 90 degrees.

0 degree < acute angle < 90 degree

Right Angle

When an angle measures to be an exact 90 degrees, it is called a right angle. It is also called a perpendicular angle.

Obtuse Angle

An obtuse angle always measures to be greater than 90 degrees but less than 180 degrees. All angles between 90 and 180 degrees are obtuse.

90 degree < Obtuse angle < 180 degree

Straight Angle

The angle between a straight line makes up a straight angle. It always measures to be an exact 180 degree.

Reflex Angle

Angle measuring greater than 180 degrees but less than 360 degrees is called a reflex angle. All reflex angles are situated between 180 and 360 degrees.

180 degree < Reflex angle < 360 degree.

There are also some types of angles that only a pair of angles could make. They are:

Complementary Angles: Two angles that add up to form 90 degrees are called complementary angles. For example, if angle ABC and angle QPR are complementary angles, then; Angle ABC + Angle QPR = 90 degree.

Supplementary Angles: When the sum of two angles makes up 180 degrees, they are supplementary angles. Suppose if angle ABC and angle QPR are supplementary, then:

Angle ABC + Angle QPR = 180 degree

Adjacent Angles: Two angles are said to be adjacent if they satisfy the following conditions:

The two angles must originate from a common vertex.

The two angles must have a common arm.

The two angles' non-common arms are situated on opposite sides of the common arm.

If angle ABD and Angle CBD are two adjacent angles with BD as their common arm, then rays AB and CB must be situated opposite the common arm BD. Also, Angle ABD + Angle CBD = Angle ABC.

Vertically Opposite Angles: When two lines intersect, there form four angles between them. Pair of angles in which one is situated opposite the other forms vertically opposite angles. Vertically opposite angles are always equal.

Discussion about lines cannot be complete without mentioning intersecting and non-intersecting lines. Intersecting lines are those which meet up or cross and pass so that they make angles between them. But, non-intersecting are those that do not meet up or tend to meet at any point. They are also known as parallel lines.

Linear Pair of Angles

Linear pairs of angles are those angles that are situated adjacent to each other and also whose sum equals 180 degrees.

Parallel Lines and Transversal

A single line that intersects two or more lines, that too at distinct points, is said to be a transversal. A transversal intersects parallel and non-parallel lines.

Triangles can be considered a section of geometry itself due to their immense properties and theorems. In this chapter, we learn about two properties.

Angle Sum Property of a Triangle

According to the angle sum property of a Triangle, the sum of three angles of a triangle always equals 180 degrees.

Exterior Angle Property

According to the exterior angle property, when a side of a triangle is extended, the exterior angle thus formed with the triangle equals the sum of two opposite interior angles.

In Daily LifeÂ

The concept of lines and angles, or in short geometry itself, is a widely used part of all our daily lives. We can find different types of lines and angles in most of the things around us. When it comes to constructing a new house, road, or building, irrespective of the construction, we need a plan made of lines and angles. In short, we can find lines and angles in each corner of our lives.

MCQs can always clarify concepts and help us check our own knowledge of any topic. Lines and Angles Class 9 MCQs can provide an in-depth understanding of how much you have conquered in the topic. Here we provide some examples too.

1) If ABC and PCQ are vertically opposite angles and ABC measures 60 degrees, how much is PCQ?

A) 90 B) 30 C) 60 D) 45

Sol: 60

2) If the exterior angle of a triangle in 120 degrees and one of its opposite interior angle is 70, how much is the other opposite angle in the triangle

A) 50 B) 120 C) 45 D) 30

Sol: 50

FAQ (Frequently Asked Questions)

Q1. How can we Find the Adjacent Angle to Exterior Angle Using Exterior Angle Property only and not Angle Sum Property?

Ans: Adding up the two opposite interior angles will measure the exterior angle. As the exterior angle and the internal angle lie adjacent and make up a liner pair, subtracting the exterior angle from 180 degrees can give us the measure of the interior angle adjacent to the exterior angle.

Q2. Angle ABC and Angle DBC make up a Pair of Complementary Angles. If Angle ABC Equals 30 Degrees, how can we Find Angle DBC?

Ans: Complementary angles are a pair of angles whose sum is 90 degrees. We are given that angle ABC is 30 degrees, and we also know their sum is 90 degrees. So by subtracting ABC from 90 degrees gives the measurement of DBC. 90 - 30 = 60 degree = DBC.