Chapter 6 - Section 6.2 - Cardinality - Exercises - Page 417: 62

"$\cup$" (union of sets)

Work Step by Step

Looking at the CardinaIity of a Union, If A and $B$ are finite sets, then $n(A\cup B)=n(A)+n(B)-n(A\cap B)$. If A and B are disjoint, their intersection is empty, so, in that case, $n(A\cup B)=n(A)+n(B)$ implying that "$\cup$" (union) could represent "sum" of disjoint sets.

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