The total number of subsets of a Finite Set containing n elements is 2ⁿ

Theorem 3   
      The total number of subsets of a finite set containing n elements is 2ⁿ.   
Proof
   Let A be a finite set containing n elements.Let 0 ≤ r ≤ n. Consider those subset,of A that  have r elements each.We know that the number of ways in which r elements can be chosen out   of n elements is nCr . Therefore, the number of subsets of A having r elements each is nCr . Hence,   the total number of subsets of A is    nC0 + nC1 +nC2 +… +nCn = (1 + 1)ⁿ = 2ⁿ   [By binomial theorem ]   
We will discuss later in permutation and combination chapter in brief.

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