For any two sets A and B, prove that

A (B – A) = A B

Let x ϵ A (B –A) x ϵ A or x ϵ (B – A)


x ϵ A or x ϵ B and x A


x ϵ B


x ϵ (A B) [ B (A B)]


This is true for all x ϵ A (B–A)


A(B–A)(AB)……(1)


Conversely,


Let x ϵ (A B) x ϵ A or x ϵ B


x ϵ A or x ϵ (B–A) [ B (A B)]


x ϵ A (B–A)


(AB) A(B–A)……(2)


From 1 and 2 we get…


A (B – A) = A B


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