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Question

If the following Boolean expression is reduced, what will be the reduced result?

(B + BC) (B + B̅C) (B + D)

The correct answer is

B

To reduce the given Boolean expression, we will apply fundamental Boolean algebra laws step-by-step. The expression to be reduced is:

\((B + BC) (B + \bar{B}C) (B + D)\)

Boolean Expression Simplification

We will simplify each term of the Boolean expression individually first, and then combine them to find the final reduced result.

First Term: Simplifying \((B + BC)\)

The first part of the Boolean expression is \((B + BC)\). This can be simplified using the Absorption Law. The Absorption Law states that \(A + AB = A\).

  • Let \(A = B\).
  • Then, \((B + BC)\) becomes \(B\).

So, the first term reduces to \(\mathbf{B}\).

Second Term: Simplifying \((B + \bar{B}C)\)

The second part of the Boolean expression is \((B + \bar{B}C)\). This can be simplified using the Consensus Theorem (also known as the Simplification Theorem or Postulate 1.8 in some texts). The Consensus Theorem states that \(A + \bar{A}B = A + B\).

  • Let \(A = B\).
  • Let \(B = C\).
  • Then, \((B + \bar{B}C)\) becomes \(B + C\).

Alternatively, we can use the Distributive Law \(A(B+C) = AB + AC\) and then the Complement Law \(A + \bar{A} = 1\):

  • \((B + \bar{B}C) = (B + \bar{B})(B + C)\) (Distributive Law)
  • We know that \((B + \bar{B}) = 1\) (Complement Law)
  • So, \((1)(B + C) = B + C\)

Thus, the second term reduces to \(\mathbf{B + C}\).

Combining and Further Reducing the Boolean Expression

Now, substitute the simplified terms back into the original Boolean expression:

\((B) (B + C) (B + D)\)

Reducing \((B) (B + C)\)

We now consider the first two terms: \((B) (B + C)\). This can again be simplified using the Absorption Law. The Absorption Law also states that \(A(A + B) = A\).

  • Let \(A = B\).
  • Then, \((B) (B + C)\) becomes \(B\).

So, the expression simplifies to \((B) (B + D)\).

Reducing the Final Expression \((B) (B + D)\)

Finally, we have \((B) (B + D)\). Applying the Absorption Law \(A(A + B) = A\) one more time:

  • Let \(A = B\).
  • Then, \((B) (B + D)\) becomes \(B\).

Therefore, the completely reduced result of the Boolean expression is \(\mathbf{B}\).

Summary of Boolean Laws Used

The following Boolean algebra laws were crucial in reducing the expression:

Law Name Expression Description
Absorption Law \(A + AB = A\) A term absorbed by itself with another variable through OR.
Absorption Law \(A(A + B) = A\) A term absorbed by itself with another variable through AND.
Consensus Theorem (or Simplification Theorem) \(A + \bar{A}B = A + B\) A term ORed with the AND of its complement and another variable.
Distributive Law \(A + BC = (A + B)(A + C)\) Distributing a variable over an AND operation (used for alternative simplification of second term).
Complement Law \(A + \bar{A} = 1\) A variable ORed with its complement results in 1.

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Important Questions from Laws of Boolean Algebra

  1. Method of subtraction by an additive approach is known as ______ subtraction.

  2. Which type of Boolean algebra law do the following laws belong to?

    Law 1: A + A.B = A

    Law 2: A(A + B) = A

  3. The equality (A + B + C)I = AI.BI.CI is better known as _______

  4. What is the minimum number of NAND gates required to implement \( A +A\bar{B} + AB\bar{C}\)?

  5. Find out the equivalent of A + A' + B'.

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