Class 4 Maths Geometry (Complete Chapter)

[Music] hello students welcome to our channel learning notebook in today's video we will do each and every concept of geometry for class 4. we have made videos on every chapter of class 4 mathematics students you can find them on our channel learning notebook also you can see a list of all such videos on our website as well the link to our website is below in the description box so let's see what all topics we are going to cover today in this geometry video first we will understand about point line and line segment then way and angles and types of angles types of lines circles its radius diameter and length and then we will learn about curves and polygons students we will cover all these topics with lots and lots of exercise so let's start and first understand what is point line and line segment first is point point is the basic unit of geometry a point shows an exact location it has no dimensions that means a point has no length breadth or high a point is represented by a dot and it is named with a capital letter for example this is point a point b and point x so how do we read this as i just told you we will read them as point a point b and point x and how do we write these points we will write them as a b and x let me tell you a real life example of a point for example location of any address on map is a point next is line segment a line segment is a straight path between two points it is the shortest distance between two points for example there are two points d e so line segment is the straight path between these two points now let me show you how to read and write line segment we will read it as line segment d e or line segment e d both the ways are fine similarly we can either write it as d e or e d with the small line segment on it also students do remember that a line segment has a definite length now let's see some real life examples of line segment edges of duster or edges of a ruler they are line segment because they have a definite [Applause] length students we have a video on complete chapter of flexions i am sure all your doubts related to flexion could be resolved after watching this video the link to this video is below in the description box now let's understand what is line a line is a set of points which extends forever in opposite directions for example this is a line the arrow on its both sides represent that a line goes indefinitely in both the directions so students it means a line has no fixed length now let me tell you how to read and write a line for this we need to take two points let's take g and h so we read a line as line gh or line hd both the ways are fine similarly we can write it as gh or hd with a small line drawn on a now students to devise these concepts let's do an exercise here we need to identify line and line segments first take a look at figure a a is not a straight path so it is neither a line segment nor a line now take a look at figure b it has two end points and has a definite length so it means it is a line segment next look at the figure c it has two arrows so it means it is never ending therefore it is a line and the last figure again the last figure is not a straight path so it is neither the line segment not a line so students now i hope you have understood the difference between line and line segments now let's do one more exercise here again we need to identify line and line segments look at figure a can you tell me whether it is a line or the line segment yes it is a line segment because it has two end points now what about figure b it is a line because it has two arrows so it means it it is never ending now let's move to figure c again this is a line segment now what about figure d it is not a straight path so it is neither a line nor a line segment students we have a separate video on complete chapter of shapes and patterns i am sure all your doubts related to this chapter would be resolved after watching this video and also notice that we have lots of quizzes and worksheets available on our channel for each chapter for class 4 so do check out them on our channel now let's do section 2 ways and angles first let's understand what is ray away is a part of the line that has a starting point and it goes on forever in one direction it means way also has no fixed length it cannot be measured for example this is a way it has a starting point called k and it goes indefinitely in one direction towards j now let me show you how to read and write way we will read the starting point first so it will be read as we kj the students there is only one way to read they that is by reading the starting point first and now how to write it we will write it kj with a small way drawn over it now let's see some real life examples of way ways from sun angry is from flashlight these are examples of ray because they have a starting point and they go indefinitely in one direction now in section three we will learn about angles two days having a common end point is called angle for example here the a b and a ac are forming an angle the two rays are called arms of the angle and the common end point is called vertex of the angle so students a is the vertex here while ac and a b are arms of the angle now let's learn how to name an angle to name an angle we need three points and the point at which an angle is formed will always be in the middle here angle is formed at vertex a so a will always be in the middle while naming this angle so we can read and write this angle as angle a or angle cab or angle bac now let's see what is interior and exterior of an angle let's consider an angle cab so this shaded region is the interior of angle cab while the rest of the area is considered to be exterior of an angle so let's take a point i this point lies in the interior of an angle while the point e lies in the exterior of the angle and other points like p and q they lie on the angle c a b now to revise these concepts let's do an exercise how many angles are formed in this figure students look at this figure carefully we can see only three angles in this figure or do we have more angles formed in this figure let's check it out first angle which we can see is angle bac second angle being formed here is angle c a d and third angle is angle d a e now look carefully we have another angle which is called angle c a e then fifth angle being formed here is angle b a b and last angle being formed here is angle b a e so it means six angles are being formed in this figure now let's learn about types of angles first let me tell you a little bit about measuring angles measure of an angle is the distance between its two arms you can measure angles in degrees using a protector we will learn how to measure angles using a protector in another video but for now you understand that angle is measured in degrees now let's learn types of angles first is right angle the measure of right angle is 90 degree as shown here this is a right angle now next type of angle is acute angle as you can see this angle measures less than 90 degree so measure of acute angle is always less than 90 degree the third type of angle is obtuse angle measure of obtuse angle is more than 90 degree but less than 180 degree and the last type of angle is straight angle the measure of straight angle is exactly 180 degree as you can see here now let's summarize types of angles first is right angle which measures exactly 90 degree and it forms a square corner second is acute angle which always measures less than 90 degree third type is obtuse angle which measures more than 90 degree but less than 180 degree and the last type of angle is straight angle which measures exactly 180 degree now students let's do an exercise based on types of angles question is state whether the angle given below is right acute obtuse or straight angle students as you can see this angle measures exactly 90 degree so it is a right angle let's see the next figure here the angle measures less than 90 degree so it will be an acute angle now have a look at this figure here the angle measures exactly 180 degree so it is a straight angle now let's see the next figure here the angle measures more than 90 degree but less than 180 degree so it is an obtuse angle now let's understand types of lines first type is intersecting lines intersecting lines are the lines that meet or cross at a common point like here line a b and line cd are intersecting at a common point e next type is perpendicular lines perpendicular lines are also intersecting lines but they intersect to form four right angles as you can see here line cd is perpendicular to line a b and they are intersecting at point e to form four light angles we have a special symbol to denote perpendicular lines so we will write line cd is perpendicular to line a b so this is the symbol of perpendicular lines now third type of lines are parallel lines parallel lines are lines in the same plane that never intersect as you can see on the screen line a b and line cd are parallel lines they will never intersect each other we have a special symbol to denote parallel lines so we will write line a b is parallel to line cd so the symbol in red is a symbol of parallel lines students we have a separate video on complete chapter of time and calendar for class 4. do watch this video now our next topic is circles students this is a circle some of the real life examples of a circle are button pizza doughnuts etc the middle point of a circle is called center as you can see in this figure this is a center of the circle and center of the circle is usually denoted by capital letter o now let's understand what is diameter the line segment passing through the center and has both end points on the circle is called diameter of the circle like here a b is the diameter of this circle as it is passing through the center and has both end points a and b on the circle students do remember the diameter of a circle can be drawn horizontally vertically or even slanting lines but it should always pass through center of the circle a diameter divides a circle into two equal parts and each part is called semicircle like here this diameter is dividing the circle into two semi circles similarly this vertical diameter divides the circle into two semi-circles and in the same way the slanting diameters divide the circle into two semi-circles now what is radius of a circle a line segment with end points at the center of the circle and on the circle is called a radius for example here o a is the radius of the circle similarly ob is also the radius of this circle because one point is at the center of the circle and other point is on the circle so students it means a circle can have more than one radius here o a ob oc od all these are radii of this circle now let's understand relation between radius and diameter diameter equals to 2 into radius or we can say radius equals to half of diameter you can easily learn the relationship between diameter and radius with the help of table of 2. if radius is 2 then diameter will be 4 similarly if the radius is 4 then diameter would be twice of 4 that is a and if radius is 8 then diameter would be equal to 16. now next is circumference length of the circle is called its circumference that means the boundary of the circle is called its circumference now students do remember that all the points on the circle are equidistant from the center eq distance means at equal distance so here all the points on the circle like a b and c they are at equal distance from center o now let's do an exercise based on the concepts of circle use the circle below to answer the questions first question is name the circle and its center remember that a circle is always named by its center so first let's see its center is v so we will write point v is the center of circle v second question is how many diameters are shown in this circle and name the diameters so students as i told you diameters they pass through center of the circle and has both end points on the circle so let's look for such line segments have rs line segment tw and line segment pq so there are three diameters of this circle third question is is tr a radius explained by or why not tr is not the radius of a circle because it's one of the end points is not the center of the circle and the last question is how many radii are shown here and name the radii so first of all what is radii the pluto of radius is radii so let's look for radii here so we have to look for line segments which have one end point at the center and other end point on the circle so line segment vq v w v s v p v t and v r these are six radii shown in this circle students we have a complete chapter of money for class 4. i am sure all your doubts would be dissolved after watching this video the link to this video is here on the top and in the description box now our next topic is curves and polygons students you must have doodled on a piece of paper some of the results of these drawings are shown here on the screen these drawings are called curves so what are simple curves a curve that do not cross itself is called a simple curve so here figure 1 2 3 are simple curves but figure 4 is not a simple curve because it is crossing itself now simple curves are of two types open curves and closed curves open curves are the curves which do not end where they start for example curves of the bridge are perfect example of open curves closed curves are the curves which end where they start for example curves of orbiting planets the orbits end where they start so this is an example of closed curves now let's do an exercise based on curves right through all falls use the picture below the statement is some of the simple closed curves are green we know simple closed curves and where they start and they do not cross themselves so yes these are simple closed curves so the statement is true now the second statement is none of the simple closed curves are blue so this statement is true because some of them are crossing each other and some are not ending where they start now the third statement is all circles are simple closed curves so this statement is also true and the last statement is none of the simple closed curves are there this statement is false because all of the figures in red are simple closed curves now students our next topic is polygons polygons are simple and closed curves that are made of only straight line segments let's take few examples to understand polygons this figure is a simple curve closed curve and is made of only line segments so this is a polygon now let's take a look at the second figure this figure is a simple curve closed curve but it is not made of only line segments so this is not a polygon third figure it is a simple curve made of only line segments but it is not a closed curve so it is not a polygon now the last figure it is a closed curve made of only line segments but it is not a simple curve so again this is not a polygon polygons are named according to number of sides or angles for example polygon with three sides or three angles is called triangle polygon with four sides of four angles is called quadrilateral square and rectangle are examples of quadrilateral polygon with five sides of five angles is called pentagon next polygon with six sides or six angles is called hexagon you can easily remember hexagon from six as both words hexagon and 6 have letter x common now polygon with 7 sides or 7 angles is called septagon you can remember septagon from seven as both words septagon and seven have initial letters s e next polygon with eight sides or eight angles is called octagon you can remember octagon from word octopus as we all know that an octopus has eight arms next a polygon with nine sides or nine angles is called nonagan you can easily remember it from 9 as both start from letter n and lastly a polygon with 10 sides or 10 angles is called decagon so students in this video we learned all the concepts related to geometry and we did lots of exercise on each of these concepts if you enjoyed this video then do share it further thanks for watching see you in the next video bye

Channel: Learning Notebook

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Length: 33min 17sec (1997 seconds)

Published: Tue May 25 2021