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Boolean Identities

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Boolean Algebraic Identities

Boolean Addition and Subtraction

Complementary Gates (NOT) Boolean complementation finds equivalency in the form of the NOT gate, or a normallyclosed switch or relay contact:

Topic Notes: • Boolean addition is equivalent to the OR logic function, as well as parallel switch contacts. • Boolean multiplication is equivalent to the AND logic function, as well as series switch contacts. • Boolean complementation is equivalent to the NOT logic function, as well as normallyclosed relay contacts.

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Boolean algebraic identities The algebraic identity of x + 0 = x tells us that anything (x) added to zero equals the original ”anything,” no matter what value that ”anything” (x) may be. Like ordinary algebra, Boolean algebra has its own unique identities based on the bivalent states of Boolean variables. The first Boolean identity is that the sum of anything and zero is the same as the original ”anything.” This identity is no different from its real-number algebraic equivalent:

No matter what the value of A, the output will always be the same: when A=1, the output will also be 1; when A=0, the output will also be 0. The next identity is most definitely different from any seen in normal algebra. Here we discover that the sum of anything and one is one:

Next, we examine the effect of adding A and A together, which is the same as connecting both inputs of an OR gate to each other and activating them with the same signal:

Introducing the uniquely Boolean concept of complementation into an additive identity, we find an interesting effect. Since there must be one ”1” value between any variable and its complement, and since the sum of any Boolean quantity and 1 is 1, the sum of a variable and its complement must be 1:

Just as there are four Boolean additive identities (A+0, A+1, A+A, and A+A’), so there are also four

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