CLASS XII MH – PCMB Maths Logic Demo Videos

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Hello Students in the previous module you were know  where the boy was simply switching on and of that switch , yes class and that was nothing but introduction to logic here we are going to advanced  knowledge in logic we are going to learn about close sentences and open Sentences yes ready for it here we have some sentences in front of you and the first one comes every triangle has three sides yes class if I ask about that whether it’s true or false what will you say obviously each triangle has three sides and that simply means the given sentences are true sentence yes class now here if I get to an example 3 is an even number now ask you is it actually even number what will you say no, it’s an odd number yes class if I ask you is the given statement true false what will you say You say it’s a  false sentence yes class such sentences which are having some truth value true value means either can be true or it can be a false yes class such sentences which is either true or false are called as closed sentences now came to know close sentences now for try to get another example in front of you a little example be, he is my brother who he, he can be Ramesh yes he can be Suresh oh you get me any one any person and that simply says he is variable able he can change its value he can be anything yes class so if i ask you whether this sentence is true or False you absolutely cannot decide about that yes because you do not know whether that he is what yes class now the next example X plus 3 is equal to seven what do you say about the sentence what does that X here has an x value given to you here know, now if i try to assume some values of x let that X be three so according to that 3, 3 plus 3 gives you six not seven and that simply means it will be nothing but false  sentence now class if i try to change the value of x if it can be 4 so 4 plus 3  let’s give you seven and that simply means it is a true sentence  now  that says for different values of X you have different output different truth value that is it can be true or it can be false yes class so you cannot see the truth value if I ask you yes there are simply says x is a variable X changes its value and according to that value it can be true or it can be false that simply says the value that is again be true or false is not fixed and therefore class for such type of question for such type of Sentence you cannot decide and what is so similar between this two sentences class this two sentences are nothing but true or false depending on the variable here and such sentences are called as open sentences such sentences which is true or false on different values of x on the different values of he nothing but called as open sentences so now you have understood very well event what do you mean by closed and open sentences now if I talk more about close two sentences if I try to give you some more examples about clothes sentences for example today is Tuesday no class for this example if I ask you is it true or false yes it’s Tuesday today and that simply means it true to sentence yes now just a minute wait if i give you another example and the example is every square consists of four sides and not far ask you is it true or false what will you say, ya mathematically it’s true yes it true sentence so this – two but you’re close sentences because they are having either truth value true or false yes class but I see that there’s a difference between this two sentences and how we are going to see just now for the first statement for the first sentence today is Tuesday class one of the some days after for example tomorrow it will be Wednesday  and if I ask you well that remains Tuesday the only know that simply means the truth value will change to false  and it simply means your true or false value is not fixed for such sentence the true or false value is not fixed while for this sentence class if I asked you tomorrow  what about the sentence if I ask you whether it’s true or false what do you say it will mean true always when I ask you tomorrow day after tomorrow it will always remain true and that simply says that it’s true or false value is fixed so that’s the difference you observe for this two sentences and such sentences where true or false value is fixed are simply called as logical Statements yes class a very important definition to remember logical statement. the truth value is fixed that means a statement is true or false and will remain the same throughout it will not change then we call it to be a logical statement   we are going to learn more about logical statements in the next models till then thank you.

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