# 6 Math Chapter 4 Basic Geometrical Ideas

Chapter Notes and Summary
• A point does not have any length, breadth and thickness. It determines a location.
• A part of a line is called a line segment. It is shortest distance between two points;
• If two distinct lines meet at a point, they are called intersecting lines.
• Two parallel lines in a plane do not meet each other.
• A drawing (straight or non-straight) drawn without lifting pencil is called a curve.
• A closed curve made up of line segments only is called a polygon. In a polygon, line segments are called its sides.
• meeting point of a pair of sides in a polygon is called a vertex of polygon.
• A three-sides polygon is called triangle. It is polygon with least number of sides.
• A four-sides polygon is called a quadrilateral.
• An angle is made up of two rays starting from a common end point. common point is called its vertex.
• A chord of a circle is a line segment joining any two points on circle.
• A diameter is a chord passing through centre of circle.
• A diameter of a circle divides its into two semi-circles.
• Diameter is longest chord of circle.
• A sector is a region in interior of a circle enclosed by an arc on one side and a pair of radii on other two sides.
• A segment of a circle is a region in interior of circle enclosed by an are and its corresponding chord.
• Every angle of convex quadrilateral is less than 180º whereas in a non-convex (or concave) quadrilateral there exists at least on angle whose measure is greater than 180º.
• Three or more lines in a plane are said to be concurrent if all of them pass through same point.