Basic Geometrical Ideas Summary Class 6 Maths Chapter 4

Introduction

• The term ‘Geometry’ is the English equivalent of the Greek word ‘Geometron’. ‘Geo’ means Earth and ‘metron’ means Measurement.

Point

• A point determines a location and has no length, breadth and height. Usually denoted by a single capital letter like A, B, C.

Line Segment

• A part of a line is called a line segment. It is the shortest distance between two points.

A Line

• A line is a straight one- dimensional figure that has no thickness and extends endlessly in both directions.

Intersecting Lines

• If two lines have one common point, they are called intersecting lines.

Parallel Lines

• Two parallel lines in a plane do not meet each other.
• The perpendicular distance between two parallel lines is the same throughout.

Curves

• Any drawing (straight or non straight) done without lifting the pencil. This means, in mathematics, a line is also a curve.
• A simple curve is one that does not cross itself.
• A curve is said to be closed if its ends are joined.
• A curve is said to be open if its ends are open.
• Polygon is a simple closed curve made up of line segments. Sides: The line segment forming a polygon.
• Vertex: The meeting point of a pair of sides.
• Adjacent sides: Any two sides with a common end point.
• Adjacent vertices: The end points of the same side of a polygon.
• Diagonal: The line joining any two non-adjacent vertices.

Angles

• An angle is made up of two rays starting from a common initial point.
• The two rays forming the angle are called the arms or sides of the angle.
• The common initial point is the vertex of the angle.
• A triangle is a three-sided polygon.
• A four sided polygon is a quadrilateral. It has 4 sides and 4 angles.

Circles

• A circle is a simple closed curve which is not a polygon.
• The path of a point moving at the same distance from a fixed point. The fixed point is the centre.
• Radius: A line segment that connects the centre to a point on the circle.
• Diameter: A line segment passing through the centre and having its end points on the circle.
• Chord: A line segment connecting any two points on a circle.
• A diameter is a chord passing through the centre of a circle. It is a longest chord of a circle.
• Arc: A portion of a circle.
• Sector: A region in the interior of a circle enclosed by an arc on one side and a pair of radii on the other two sides.
• Segment: A region in the interior of a circle enclosed by an arc and chord.
• Circumference: The distance around a circle.
• Semi-circle: A diameter of a circle divides it into two equal parts, each part is a semi-circle.