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| | Relations |
 | | Notice that this numerical description is not as complete as the algebraic description; there are infinitely many pairs of numbers that satisfy the equation, so we have neither time nor space to include all of them (as indicated by the vertical dots). |
 | | For example, the relation "is a sibling of" in my mother's family would consist of the set of ordered pairs: {(Isabella, John), (John, Isabella), (Isabella, Henry), (Henry, Isabella), (Henry, John), (John, Henry)}. |
 | | Note: Because these are ordered pairs, the order matters, so that (since the relationship of sibling is reciprocal) we must list both ordered pairs for each pair of siblings. |
| campus.northpark.edu /math/precalculus/Functions/Functions/Relations (524 words) |
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