 so now we are going to study classification classification of triangles now what does classification means mean classification means we want to understand different varieties and what all types of triangles are and we can club them together and probably study them yeah so there are two ways what we are going to take classification of triangles in this series so one is on the basis of so there must be some basis of classification on the basis of side length or the edge length okay so this is going to be first classification and the second classification is going to be on the measure of the angle measure of the angles okay so on the basis of let's take the first one on the basis of on the basis basis of side length so we have categorized triangle into three categories one is called scale and triangle scale and triangle what is scale and triangle a triangle a triangle with all sides of different length is called a scale and triangle okay so all sides with different length will be called scale and triangle second one is isosceles triangle isosceles triangle what is that iso means same and sillies scale is right isosceles triangle means same side iso means same so there are two equal sides two equal sides in one triangle then the third the third one should not be equal only two one triangle right then it's called isosceles and third one is equilateral triangle equilateral triangle so as the name suggests equi means same lateral means side so all sides equal right so what is the definition here or identification is all sides are equal this is on the basis of side length so you can see if I draw like this this is a scale and triangle right no two sides are equal so ab and c so ab length is not equal to bc not equal to ca that's scale and triangle what about isosceles triangle so if you see this is an isosceles triangle so let's say ab and c and ab is equal to so you can say ab is equal to ac isosceles but not equal to bc right and third one equilateral triangle so you can see equilateral triangle you can draw equilateral triangle like that so I'm rough you know roughly this would be like that abc where all the sides are equal this is equal to this is equal to this correct so you can say ab is equal to bc is equal to ca this is equilateral triangle now the second categorization was or the second classification was on the basis of angles isn't it on the basis of angles okay so there are again three category one is acute angle triangle acute angle triangle what is this on the basis of angles so now we are measuring the angles and basis of that we are going to classify triangles acute angle triangle is a triangle a triangle with all angles less than 90 degrees now why are they called acute then so acute literally means sharp so acute means very sharp so sharp means pointed in this case so hence angles are sharp so all of them are less than 90 degrees okay then we get acute angle so where do you see acute angle so in your kitchen if you go you will see knives the knife edge is so acute isn't it this looks like a right angle triangle so let me just change it a little bit so let me draw like this right so this is an acute angle triangle right all edges look slow look so sharp right so the pointed and sharp so acute angle triangle abc right abc is acute angle triangle now second category is right angled right angled triangle now this nomenclature is is since euclid's time or even before that actually there is right line as well so the line joining two points it's called a right line so right angled triangle what is the right angle so what you now know as a perfect 90 degree angle so this is a one angle is 90 degree then it is called a right angled triangle right abc so what is the right angle to triangle angle if one angle if one angle is equal to one of the three 90 degree you can't have more than one angle so you can note can't have more than one right angle one right angle inner triangle we'll prove it a little later but understand this right so can't have more than one right angle in a triangle so that is right angle triangle and third one is obtuse angle triangle obtuse angled triangle okay what does it mean so it means that at least one angle should be greater than 90 degree should be one angle only in acute angle triangle we talk about all three should be less than 90 degree in this one angle should be greater than 90 degrees automatically the other two will become lesser than 90 degrees that's also we are going to study so if you see what how does obtuse angle triangle look like so this is a obtuse angle triangle abc abc this is more than 90 degrees okay so angle abc in this case is more than 90 degrees why it is called obtuse obtuse means blunt so if you have a knife with that kind of an angle at its edge you will not be able to use the knife properly so obtuse blunt acute sharp and right you always know perfect you know l-shaped angle right so this is what is the classification of triangles now we are going to take up uh theorems on triangle right theorems are nothing but you know some facts about any particular a mathematical concept where we can prove them by logic okay so that's what we are going to take up next