prove its true: |A union B| = |A| + |B| – |A intersection B|

[OSMAN]

Prove $\displaystyle |A\cup B|=|A|+|B| - |A\cap B|$

 

[HallsofIvy]

Divide A and B into three sets: all x that are in A but not B, all y that are in B but not A, all z that are in $\displaystyle A\cap B$. Show that that every member of A and B is in one and only one of those.

 

[pka]

Prove $\displaystyle |A\cup B|=|A|+|B|-|A\cap B|$

If $\displaystyle X,~Y,~\&~Z$ are three pairwise disjoint sets then $\displaystyle |X\cup Y\cup Z|=|X|+|Y|+|Z|$
$\displaystyle |(A\setminus B)|=|A|-|A\cap B|$

If you understand that the show that $\displaystyle (A\cup B)=(A\setminus B)\cup (B\setminus A)\cup (A\cap B)$

 

[mivi]

If $\displaystyle X,~Y,~\&~Z$ are three pairwise disjoint sets then $\displaystyle |X\cup Y\cup Z|=|X|+|Y|+|Z|$
$\displaystyle |(A\setminus B)|=|A|-|A\cap B|$

If you understand that the show that $\displaystyle (A\cup B)=(A\setminus B)\cup (B\setminus A)\cup (A\cap B)$

Full ans ?

 

[mmm4444bot]

Full [answer] ?

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[khansaheb]

Prove $\displaystyle |A\cup B|=|A|+|B| - |A\cap B|$

Look up into your text book for "elementary set theory". This is a rudimentary theorem - every text book that I know of states it and proves it.