addition, fundamental operation of arithmetic, denoted by +. In counting, a + b represents the number of items in the union of two collections having no common members (disjoint sets), having respectively a and b members. In geometry a + b might, for example, represent the area of the union of two disjoint regions of areas a and b, respectively. In arithmetic addition follows the associative law , the commutative law , and, in combination with multiplication, the distributive law . Addition is also defined for other types of mathematical objects, for example, vectors and tensors . See also subtraction .
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