[Math] Two uncountable sets A and B are countably infinite

elementary-set-theory

I'm having trouble finding the solution to the following problem…

Give an example of an uncountable set $A$ and an uncountable set $B$ such that $A$ intersect $B$ is countable infinite.

Answer – I know that $(-\infty, 1]$ and $[1, \infty)$ has an intersection of $\{1\}$. $\{1\}$ is countable but $\{1\}$ is also finite. I need to find two sets that have a result of countably infinite. Thanks guys!

Best Answer

HINT: Can you find two uncountable sets which are disjoint? Now find a countable set and add it to both of them.

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