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Let A and B be sets. If `A nnX = B nnX =varphi`and `A uuX = B uuX`for some set X, show that `A = B`.(Hints `A = A nn(A uuX), B = B nn(B uuX)`and use Distributive law) |
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Answer» Let sets A and B are such that, for any set X, `A cupX=BcupX` `rArrAcap(A cupX)=A cap(BcupX)` `rArrAcap(A cupX)=(A cap B)cup (A cap X)` (From distributive law) `rArrAcap(A cupX)=(AcapB)cup phi(becauseA capX=phi)` `rArrA=(AcapB)cupphi` `rARr A =(A capB)`...(1) Again for any set X, `A cup X = B cup X` `rArr B cap (A cup X)=B cap (B cup X)` `rArr (B cup A)cup(B cap X)=B cap (B cup X)` (From distributive law) `rArr(B cupA)cup phi=Bcap(BcupX)[because(B capX)=phi]` `rArr(BcupA)cupphi=B` `rArr B=(B capA)` `rArr B= A cap B`....(2) From equations (1) and (2), `rArr A =B`. |
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