So guys what is A.P:- The full form of A.P is arithmetic progression the collection of the numbers.with a suitable relation is called A.P. Term related with A.P:- Let we take 3,6,9,12... Here 3 is first term of A.P so we denote it with a so a=3 a2=6 a3=9 So guys we denote the nth term with An=a+(n-1)×d Guys here is a new term d Here d is common difference. Means a2-a=d Thus a3-a2=d Here 6-3=3 9-6=3 So guys we can say that a collection of no. Is a.p if the difference between every term is same and this difference is called d or common difference Here d=5 same for all Let we take example 1,4,6,9 This is not A.P bcz here a2-a=3=d a3-a2=6-4=2 Here we can see that the common difference is not same this is not a A.P. Let we take another example -3,-5,-7,-9.... Here we find d=-2 d=-7+5=-2 So here common difference is same so this is a A.P