 Hi and welcome to the session. Let us discuss the following question. It states write the following intervals in set builder form. Now in all these four cases you need to write them in set builder form but let us be well versed with these types of brackets. It says that in an open interval we have our elements denoted by this and all the points between A and B belongs to the open interval but A and B themselves do not belong to this interval. That means if we will be writing about X, so it will be greater than A and less than B. Right? That means excluding A and B whereas in an closed interval if we write AB are the elements then A and B themselves are belonging to this interval. That means X is greater than equal to A and less than equal to B. Right? The knowledge of these intervals will help us in the solution and here we represent them by these brackets. So these are the key ideas that is going to help us in the following question. So first of all we are given minus 3 0 and it is an open interval so we need to write them in set builder form. So it will be X is to X and here we have minus 3 and 0. So it will be X is to X. It belongs to real number and X is greater than minus 3 but less than 0. Right? Got it because here we have written only greater than or less than sign but not an equality sign because it was an open interval question. B part we have closed interval and the elements are ranging from 6 to 12. So here we will be writing X is to X belongs to R and X is greater than equal to 6 but less than equal to 12. Now here 6 and 12 are included in this set. So here is the difference between an open interval and a closed interval. When we are given both the intervals in one question then it says that 6 is not included but 12 is included and we write it in such a way that X is to X belongs to real number where X is greater than 6 but less than equal to 12 because here it is a closed interval as 12 will be included but 6 will not be included. So I think you are getting my point very clearly and here if we have something like minus 23 has a closed interval where 5 is an open interval we say here X is to X belongs to real number and X is greater than equal to minus 23 but less than 5. Here 5 is not included in this interval. So I hope you understood the difference between an open interval and a closed interval clearly. Try to do more examples to make your vision more clearer. Bye for now.