 Hi and welcome to the session. Today we will learn about addition and subtraction of algebraic expressions. Consider an algebraic expression 3xy plus 5x square y minus 2xy square plus 7xy plus 9. Here we can clearly see that 3xy and 7xy are like terms. So first of all we need to know that like terms can be added or subtracted and unlike terms cannot be added or subtracted. So they are left as they are. Now let us add these two terms that is 3xy and 7xy. So let us see how to add two like terms. We have 3xy plus 7xy and these first of all consider the numeric coefficient of both the terms which is 3 and 7 over here. So let us add 3 and 7 and now we will write xy as it is. So we get 3 plus 7 that is 10xy. Now as we have added these two terms so let us rewrite this expression as 10xy plus 5x square y minus 2xy square plus 9. Now here as all other terms are unlike terms so we have left them as they are. Now let us see how to subtract like terms. Suppose we want to subtract 3xy from 7xy. So 7xy minus 3xy will be equal to here again consider the numeric coefficient of both the terms and subtract them so we get 7 minus 3. Now we will write xy as it is so we get 4xy. Now we know that sum of two or more like terms is a like term with a numerical coefficient equal to the sum of the numerical coefficients of all the like terms and difference between two like terms is a like term with a numerical coefficient equal to the difference between the numerical coefficients of the two like terms. So let us see how to add and subtract general algebraic expressions. Suppose we want to subtract the algebraic expression a square minus 2b square plus 6ab from the algebraic expression 2a square minus 3b square plus 6ab then 2a square minus 3b square plus 6ab minus a square minus 2b square plus 6ab will be equal to here first of all we will open the brackets so this will be equal to 2a square minus 3b square plus 6ab. Now we have minus sign outside the bracket so that means when we will open the bracket then all the signs inside the bracket will change and we will get minus a square plus 2b square minus 6ab. Now let us connect all like terms here 2a square and minus a square are like terms so let us write them together. Now minus 3b square and plus 2b square are like terms so we will write them also together and lastly plus 6ab and minus 6ab are like terms. Now 2a square minus a square will be equal to 2 minus 1 into a square which will be equal to 1a square that is a square. So here we will have a square. Now minus 3b square plus 2b square will be equal to minus 3 plus 2 into b square which is equal to minus 1b square and this can also be written as minus b square. So here we will have minus b square and lastly plus 6ab minus 6ab will be equal to 6 minus 6 into a b which will be equal to 0 into a b that is 0 so we have plus 0. Now this will be equal to a square minus b square thus the difference of these two algebraic expressions is a square minus b square. With this we finish this session hope you must have understood all the concepts. Goodbye, take care and have a nice day.