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Question: Answered & Verified by Expert
Let A, B and C  be sets such that ϕABC. Then which of the following statements is not true?
MathematicsSets and RelationsJEE MainJEE Main 2019 (12 Apr Shift 2)
Options:
  • A BCϕ
  • B (CA)(CB)=C
  • C If (A-B)C, then AC
  • D If (A-C)B, then AB
Solution:
1061 Upvotes Verified Answer
The correct answer is: If (A-C)B, then AB


For A=C,A-C=ϕ
ϕB
But AB
Hence, If (A-C)B, then AB is not true
Let xC,  xCACB
xCA and xCB
(xC or xA) and (xC or xB)
xC or xAB
xC or xC  asABC
xC
CACBC .... (i)
Now xCxCA and xCB
x(CA)CB
C(CA)CB ..... (ii)
From (i) and (ii)
C=CACB
Hence, (CA)(CB)=C is true
Let xA and xB
xA-B
xC asA-BC
Let xA and xB
xAB
xC asABC
Hence xA xC
AC
Hence, If (A-B)C, then AC is true
as CAB
BCAB
as ABϕ
BCϕ
Hence, BCϕ is true

Alternate solution

Given 

ϕABC

Let answer that

C=1,2,3,4,5,6

A=1,2,3

B=3,4,5

AB=3

Option (a) 

BC=3,4,5ϕ

Option (b) CA=1,2,3,4,5,6

CB=1,2,3,4,5,6

CACB=1,2,3,4,5,6=C

Option (c) AB=1,2,3CAC True

Option (d) AC=ϕB  AC Not correct

 Option (d) is correct 

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