Last Updated :
19 Nov, 2018
Let X denote the Exclusive OR (XOR) operation. Let ‘1’ and ‘0’ denote the binary constants. Consider the following Boolean expression for F over two variables P and Q:
F(P, Q) = ( ( 1 X P) X (P X Q) ) X ( (P X Q) X (Q X 0) )
The equivalent expression for F is
(A) P + Q
(B) (P + Q)\’
(C) P X Q
(D) (P X Q)\’
Answer: (D)
Explanation:
We need to simplify the above expression. As the given operation is XOR, we shall see property of XOR.
Let A and B be boolean variable.
In A XOR B, the result is 1 if both the bits/inputs are different, else 0.
Now,
( ( 1 X P) X (P X Q) ) X ( (P X Q) X (Q X 0) )
( P\' X P X Q ) X ( P X Q X Q ) ( as 1 X P = P\' and Q X 0 = Q )
(1 X Q) X ( P X 0) ( as P\' X P = 1 , and Q X Q = 0 )
Q\' X P ( as 1 X Q = Q\' and P X 0 = P )
PQ + P\'Q\' ( XOR Expansion, A X B = AB\' + A\'B )
This is the final simplified expression.
Now we need to check for the options.
If we simplify option D expression.
( P X Q )\' = ( PQ\' + P\'Q )\' ( XOR Expansion, A X B = AB\' + A\'B )
((PQ\')\'.(P\'Q)\') ( De Morgan\'s law )
( P\'+ Q).(P + Q\') ( De Morgan\'s law )
P\'P + PQ + P\'Q\' + QQ\'
PQ + P\'Q\' ( as PP\' = 0 and QQ\' = 0 )
Hence both the equations are same. Therefore Option D.
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