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III. Long Answer Questions · Q11

Q.State Boolean laws. Elucidate how they are used to simplify Boolean expressions with suitable example.

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Step 1 (The laws). Complement law: A⋅A‾=0A\cdot\overline{A}=0, A+A‾=1A+\overline{A}=1. OR laws: A+0=AA+0=A, A+1=1A+1=1, A+A=AA+A=A. AND laws: A⋅0=0A\cdot0=0, A⋅1=AA\cdot1=A, A⋅A=AA\cdot A=A. Commutative: A+B=B+AA+B=B+A, A⋅B=B⋅AA\cdot B=B\cdot A. Associative: A+(B+C)=(A+B)+CA+(B+C)=(A+B)+C, A⋅(B⋅C)=(A⋅B)⋅CA\cdot(B\cdot C)=(A\cdot B)\cdot C. Distributive: A(B+C)=AB+ACA(B+C)=AB+AC, and the Boolean-specific A+BC=(A+B)(A+C)A+BC=(A+B)(A+C).

Step 2 (Why they matter). A raw Boolean expression written straight from a circuit's wiring often has redundant terms; applying these laws algebraically reduces the expression to its simplest equivalent form, and since each term in the final expression corresponds to a physical gate, a shorter expression means FEWER gates needed to build the same logic function -- lower cost, less complexity, less power.

Step 3 (Worked example). Simplify AC+ABCAC+ABC. Factor out the common term AC: AC(1+B)AC(1+B). By OR law 2 (X+1=1X+1=1, applied with X=BX=B), 1+B=11+B=1, so the expression becomes AC⋅1AC\cdot1. By AND law 2 (X⋅1=XX\cdot1=X), AC⋅1=ACAC\cdot1=AC. Therefore AC+ABC=ACAC+ABC=AC. …

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