Question Details

Consider the following Boolean expression of a function F:


F(P,Q) = (¯P +Q)⊕(¯PQ)


Which of the following expressions is/are equivalent to F?

Options

A

P Q

B

P Q

C

P Q ¯

D

P ¯ Q

Show Answer

Correct Answer :

Option A

P Q

Option C

P Q ¯

Option D

P ¯ Q

Option C

P Q ¯

Option D

P ¯ Q

Solution :

The equivalent expressions to the given Boolean function F are:
1. PQ
2. PQ¯
3. P¯Q

Step-by-Step Derivation and Simplification:

The given Boolean expression is:
F ( P , Q ) = ( P ¯ + Q ) ( P ¯ Q )

Recall the definition of the XOR (Exclusive OR) operation. For any two Boolean variables A and B:
A B = A ¯ B + A B ¯

Let us define:
A=P¯+Q
B=P¯Q

First, let us find the complements of A and B:
1. Using De Morgan's Law for A¯:
A ¯ = ( P ¯ + Q ) ¯ = P Q ¯
2. Using De Morgan's Law for B¯:
B ¯ = ( P ¯ Q ) ¯ = P + Q ¯

Now, substitute these back into the XOR formula:
F = A ¯ B + A B ¯

Let us evaluate each term separately:
• The first term A¯B:
A ¯ B = ( P Q ¯ ) ( P ¯ Q ) = ( P P ¯ ) ( Q Q ¯ ) = 0 0 = 0
• The second term AB¯:
A B ¯ = ( P ¯ + Q ) ( P + Q ¯ )
Distributing the multiplication:
A B ¯ = P ¯ P + P ¯ Q ¯ + Q P + Q Q ¯
Since P¯P=0 and QQ¯=0, this simplifies to:
A B ¯ = P Q + P ¯ Q ¯

Combining both terms:
F = 0 + P Q + P ¯ Q ¯ = P Q + P ¯ Q ¯

The expression PQ+P¯Q¯ is the standard representation of the XNOR (Exclusive-NOR) operator:
F = P Q

Equivalences of XNOR:
The XNOR gate represents the complement of the XOR gate:
P Q = P Q ¯
Using XOR properties, complementing one of the inputs of an XOR gate complements the overall output, which makes it equivalent to XNOR:
P Q ¯ = P Q ¯ = P ¯ Q

Thus, the equivalent expressions from the given choices are:
PQ
PQ¯
P¯Q

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