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If an = {ax : x ∈ N}, then 3N ∩ 7N = |
3N 7N N 21N |
21N |
We have 3N = {3x : x ∈ N} = {3, 6, 9, 12,…} And 7N = {7x : x ∈ N} = {7, 14, 21, 28, 35, 42…} Hence 3N ∩ 7N = {21, 42, 63, ….} = {21x : x ∈ N} = 21N Hence (4) is the correct answer. |
