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Lets assume we have following subsets of $\mathbb{R}$:

$A = \lbrace 1,3 \rbrace , B=[-1,3], C = \lbrace 0, \frac{20}{7}, \frac{18}{5} \rbrace $

Let $M=A \times ( B \cap C )$

What is M written in enumeration?

What i did so far: $B \cap C = [ 0, \frac{20}{7} ]$

I hope this is correct. Now should be $M=A \times [ 0, \frac{20}{7} ]$ left.

  1. Is what i did correct?
  2. How can i continue? I've seen visual presentations of similar questions for the last part but how can i write it down?
Andrés E. Caicedo
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wolfffi
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1 Answers1

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Since $C$ is finite, $B×C$ should also be finite, and I presume this is a typo in writing what should be $\{0,20/7\}$ as $[0,20/7]$. Now its Cartesian product with $A$ follows: $$A×(B\cap C)=\{(1,0),(3,0),(1,20/7),(3,20/7)\}$$

Parcly Taxel
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  • With Ris and Alex answers it was much clearer and with your answer now i know i am right :-) Thank you very much! Will mark it as correct answer in a few minutes. – wolfffi Feb 04 '20 at 12:42