4.3.7

Boolean Identities

Test yourself

Boolean Identities

There are a number of rules that can be used to simplify boolean expressions. Simplified expressions are cheaper and easier to implement as fewer logic gates are needed.

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AND identities

  • A value AND false returns false.
    • X.0=0X. 0 = 0
  • A value AND true returns the value.
    • X.1=XX.1 = X
  • A value AND the same value returns the value.
    • X.X=XX.X = X
  • A value AND NOT the same value returns false.
    • X.X=0X.\overline{X} = 0
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OR identities

  • A value OR false returns the value.
    • X+0=XX + 0 = X
  • A value OR true returns true.
    • X+1=1X + 1 = 1
  • A value OR the same value returns the value.
    • X+X=XX + X = X
  • A value OR NOT the same value returns true.
    • X+X=1X +\overline{X} = 1
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Example

  • Using the identities, we can simplify the expression:
    • (X.X)+(X+0)(X.X)+(X+0)
    • (X.X)+X(X . X) + X
    • X+XX + X
    • XX

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1Components of a Computer

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3Exchanging Data

4Data Types, Data Structures & Algorithms

5Legal, Moral, Cultural & Ethical Issues

6Elements of Computational Thinking

6.1Thinking Abstractly

6.2Thinking Ahead

6.3Thinking Procedurally

6.4Thinking Logically

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7Problem Solving & Programming

8Algorithms

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