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Half redirects here. For the online store owned by eBay see Half.com. One half is the irreducible fraction resulting from dividing one by two (½), or any number by its double; multiplication by one half is equivalent to division by two. It is the fraction occurring most often in mathematical equations, recipes, measurements, etc. For instance, the area S of a triangle is computed S = ½ × base × perpendicular height One half also figures in the formula for calculating figurate numbers, such as triangular numbers and pentagonal numbers: ½ × n ( ( s - 2 ) n - ( 4 - s ) ) and in the formula for computing magic constants for magic squares M2(n) = ½ × ( n ( n2 + 1 ) ) One half has two different decimal expansions, the familiar 0.5 and the recurring 0.49999999... It has a similar pair of expansions in any even base. It is a common trap to believe these expressions represent distinct numbers: see the proof that 0.999... equals 1 for detailed discussion of a related case. One half is also:
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