A·B + A·B̄ — Boolean simplification

introadjacency; 1 term, 1 literal

Answer

A

Why this example is worth doing

The smallest simplification in the syllabus and the one that explains every other. B is true in one term and false in the other, and nothing else differs, so whatever B does the value follows A alone. The page names this the adjacency form of the complement law, A·B + A·B̄ = A·(B + B̄) = A·1 = A, and shows the factorisation as a separate step rather than collapsing it — students lose marks for jumping straight to the answer. It is also the algebraic twin of circling two neighbouring 1s on a K-map.

Try your own input in the Boolean algebra simplifier. Simplify any expression to its minimal SOP and POS, one named law at a time.

How the answer is reached

Step by step

A · B + A · B′A · (B + B′)Factoring (distributive, right to left) — A · B + A · C = A · (B + C)

A · (B + B′)A · 1Complement — A + A' = 1

A · 1AIdentity — A · 1 = A

Warning:

A · B + A · B′ simplifies to A in 3 steps. That is a proven minimum (1 term, 1 literal), not a best effort. It is the only minimum-cost form.

Quine–McCluskey

Prime implicants — Quine–McCluskey
#Term
1A
Minimum cover — Quine–McCluskey
#Cover
1A
Warning:

1 term(s), 1 literal(s); 1 essential prime implicant(s).

Truth table

Truth table — columns #, A, B, F
#ABF
0000
1010
2101
3111

Compare with

Open this example in the Boolean algebra simplifier

The field arrives filled in with this example’s input.

Note:

Notation this page assumes

  • Symbols: · is AND, + is OR, ⊕ is XOR, a prime or an overline is NOT. The field also takes ∧ ∨ ¬ ~ ! & | and the words.
  • Operator precedence, tightest first: NOT, then AND (including juxtaposition), then XOR/XNOR, then NAND/NOR, then OR, then IMPLIES, then IFF.
  • In a minterm index the first variable is the most significant bit, so over [A, B, C] minterm 5 is A·B̄·C.

Sources

  • Boole, An Investigation of the Laws of Thought (1854)
  • Shannon, “A Symbolic Analysis of Relay and Switching Circuits” (1938)