By-Supriya Negi

Class-IX CRoll No.-30

LINES AND ANGLES

IntroductionBasic terms and definitionsIntersecting lines and Non-intersecting

linesPerpendicular linesAnglesTypes of anglesParallel linesTransversal

CONTENT

• In our daily life, we see different types of angles formed between the edges of plane surfaces. For making a similar kind of model using the plane surfaces, we need to have a thorough knowledge of angles.

• In science, we study the properties of light by drawing the ray diagrams. For example, to study the refraction property of light when it enters from one medium to the other medium, we see the properties of intersecting lines and parallel lines.

INTRODUCTION

LINES : A straight path extending in both directions with no end points.

LINE SEGMENT : A part of a line that

includes two points, called end points, and all the points between them.

RAY : A part of a line, with one end point, that continues without end in one direction.

BASIC TERMS AND DEFINITIONS

INTERSECTING LINES : Lines that cross each other.

NON – INTERSECTING LINES : Lines that never cross each other and are always parallel to each other.

INTERSECTING LINES AND NON-INTERSECTING LINES

Two lines that intersect each other to form a right angle are called parallel

lines.

PERPENDICULAR LINES

Angle is formed when two rays originate from the same end point. The rays making an angle are called the arms of the angle and the end point is called the vertex of the angle. There are many types of angles such as :• Acute angle• Right angle• Obtuse angle• Straight angle• Reflex angle• Adjacent angles• Linear pair of angles• Vertically opposite angles

ANGLES

An angle whose measure is more than 0˚ but less than 90˚ is called an acute angle.

ACUTE ANGLE

EXAMPLES OF ACUTE ANGLES

An angle whose measure is equal to 90˚ is called a right angle.

RIGHT ANGLE

EXAMPLES OF RIGHT ANGLES

An angle whose measure is less than 180˚ but more than 90˚ is called an obtuse angle.

OBTUSE ANGLE

EXAMPLES OF OBTUSE ANGLES

An angle whose measure is equal to 180˚ is called a straight angle.

STRAIGHT ANGLES

EXAMPLES OF STRAIGHT ANGLES

An angle whose measure is more than 180˚ but less than 360˚ is called reflex angle.

REFLEX ANGLE

EXAMPLES OF REFLEX ANGLES

Angles which have one common arm and a common vertex and the uncommon arms are opposite to each other are called adjacent angles.

ADJACENT ANGLES

EXAMPLES OF ADJACENT ANGLES

Angle formed by a line intersecting a straight line is called a linear pair.

LINEAR PAIR OF ANGLES

EXAMPLES OF LINEAR PAIR

Angles formed by two intersecting lines such that the opposite angles are equal are called vertically opposite angles.

VERTICALLY OPPOSITE ANGLES

EXAMPLES OF VERTICALLY OPPOSITE ANGLES.

Parallel lines are the lines that remain the same distance apart over their entire length. No matter how far we extend them, they will never meet.

PARALLEL LINES

A transversal is a line that intersects two or more parallel lines at different points.

There are some pair of angles formed when a transversal intersects two lines such as : Corresponding angles Alternate interior angles Alternate exterior angles Interior angles on the same sides of

transversal

TRANSVERSAL

CORRESPONDING ANGLES

ALTERNATE INTERIOR ANGLES

ALTERNATE EXTERIOR ANGLES

INTERIOR ANGLES ON THE SAME SIDES OF TRANSVERSAL

END OF PRESENTATION

Thank you for watching.