4th Class Mathematics Geometrical Figures Introduction

Introduction In our day to day life we come across a number of objects. All the objects has a specific shape and size. See the following figures: (a)                                             (b) (c)                               (d) (e) We recognize a number of objects by their shapes. Therefore, to know about the objects, being aware about their shape is very important. In this chapter we will study about the shapes of different geometrical figures. Point To show a particular location, a dot (.) is placed over it, this dot is known as point. In the above figure, point A shows the location of India, point B shows the location of Australia, point C shows the location of Russia, point D shows the location of China, point E shows the location of Iran, point F shows the location of Algeria. Look at the following figure, and name the point which shows the location of Bangalore on the map? Solution: Point (e) shows the location of Bangalore on the map. Arrow and End Point Before understanding line, line segment, and ray, let us understand meaning of Arrow and End point. Ø Arrow: Arrow at end of a line segment indicates that the line can be extended up to infinity in that direction. Ø End point: End point of a line segment indicates that where does the line segment come to end. Line Segment Line segment is defined as the shortest distance between two fixed points. It is denoted as\[\overline{\text{AB}}\]. Features of a Line Segment Ø A line segment has two end points. Ø A line segment has fixed length. Ø Line segment PQ, has two end points P and Q. Ø Line segment PQ has fixed length of 5 cm. Name all the line segments given in the figure. Solution: \[\overline{\text{AB}},\text{ }\overline{\text{BC}},\text{ }\overline{\text{CD}},\text{ }\overline{\text{DA}},\text{ }\overline{\text{AC}},\text{ }\overline{\text{BD}},\text{ }\overline{\text{OA}},\text{ }\overline{\text{OB}},\text{ }\overline{\text{OC}},\text{ }\overline{\text{OD}}\] Ray It is defined as the extension of a line segment in one direction up to infinity. It is denoted as ha Features of a Ray (a) A ray has only one end point. (b) A ray has an arrow at its one end, which shows that the ray can be extended up to infinity in one direction. (c) Length of a ray cannot be measured. (a) P is the end point of the ray PQ. (b) The ray PQ can be extended up to infinity in the direction of arrow. (c) Length of the ray PQ cannot be measured as it goes to infinity in one direction. Write the name of rays given in the picture. Solution: \[\overrightarrow{\text{OD}},\text{ }\overrightarrow{\text{OC}},\text{ }\overrightarrow{\text{OA}},\text{ }\overrightarrow{\text{OB}}\text{, }\overrightarrow{\text{AD}}\text{, }\overrightarrow{\text{BC}},\text{ }\overrightarrow{\text{AE}},\text{ }\overrightarrow{\text{BE}},\text{ }\overrightarrow{\text{AF}},\text{ }\overrightarrow{\text{BF}}\] Line Line is defined as the extension of a line segment up to infinity in either direction. It is denoted as \[\] Features of a Line Ø A line has no end points. Ø A line has an arrow at its either ends which shows the line can be extended up to infinity in either direction. Ø Length of a line cannot be measured as it goes to infinity. Ø Line PQ has no end points. Ø Line PQ has arrow at its either ends thus line PQ can be extended up to infinity in either direction. Ø Length of line PQ cannot be measured as it goes to infinity. Look at the picture, find the lines and name them. Solution: \[\]