If aN = { ax:x ∈ N} , then set 3N cap 7N is ..... N

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1.Set Theory

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If $aN = \{ ax:x \in N\} ,$ then the set $3N \cap 7N$ is .....$N$

A

$21$

B

$10$

C

$4$

D

None of these

Solution

(a) $3N = \{ x \in N:x$ is a multiple of $3\}$

$7N = \{ x \in N:x$ is a multiple of $7\}$

$\therefore 3N \cap 7N$$ = \{ x \in $ is a multiple of $3$ and $7\}$

$ = \{ x \in N:x$ is a multiple of $3$ and $7\}$

$ = \{ x \in N:x$ is a multiple of $21\}=21N.$

Standard 11

Mathematics

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