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  2. Chi-squared distribution - Wikipedia

    en.wikipedia.org/wiki/Chi-squared_distribution

    In probability theory and statistics, the chi-squared distribution (also chi-square or -distribution) with degrees of freedom is the distribution of a sum of the squares of independent standard normal random variables.

  3. Cross-multiplication - Wikipedia

    en.wikipedia.org/wiki/Cross-multiplication

    In mathematics, specifically in elementary arithmetic and elementary algebra, given an equation between two fractions or rational expressions, one can cross-multiply to simplify the equation or determine the value of a variable.

  4. Taft equation - Wikipedia

    en.wikipedia.org/wiki/Taft_equation

    The Taft equation is a linear free energy relationship (LFER) used in physical organic chemistry in the study of reaction mechanisms and in the development of quantitative structure–activity relationships for organic compounds. It was developed by Robert W. Taft in 1952 [2] [3] [4] as a modification to the Hammett equation. [5]

  5. Square number - Wikipedia

    en.wikipedia.org/wiki/Square_number

    For example, =, so 9 is a square number. A positive integer that has no square divisors except 1 is called square-free. For a non-negative integer n, the n th square number is n 2, with 0 2 = 0 being the zeroth one. The concept of square can be extended to some other number systems.