A logarithm calculated using the negative or reciprocal of a number, used in mathematical calculations; the complement logarithm.
A contraction of 'cologarithm' (co- + logarithm), which combines the prefix 'co-' (complement or reciprocal) with 'logarithm.' This mathematical term emerged in the 19th century to simplify calculations.
Before calculators, mathematicians used logarithm tables to multiply huge numbers by turning multiplication into addition—cologs made division easier by letting you subtract instead, a hack that saved mathematicians hours of work per calculation.
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