Q. 11 Let A and B be sets. If A X
B
X
and A
X
B
X for some set X, show that A
B.
Given, A X
B
X
and A
X
B
X
To prove: A = B
A = A (A
X) (A
X
B
X)
= A (B
X)
= (AB)
(A
X)
= (AB)
(A
X
)
= (AB)
B = B (B
X) (A
X
B
X)
= B (A
X)
= (BA)
(B
X)
= (BA)
(B
X
)
= (BA)
We know that (AB) = (B
A) = A = B
Hence, A = B