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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. |
