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  2. Cancelling out - Wikipedia

    en.wikipedia.org/wiki/Cancelling_out

    For example, a fraction is put in lowest terms by cancelling out the common factors of the numerator and the denominator. [2] As another example, if a × b = a × c , then the multiplicative term a can be canceled out if a ≠0, resulting in the equivalent expression b = c ; this is equivalent to dividing through by a .

  3. Divisibility rule - Wikipedia

    en.wikipedia.org/wiki/Divisibility_rule

    Take each digit of the number (371) in reverse order (173), multiplying them successively by the digits 1, 3, 2, 6, 4, 5, repeating with this sequence of multipliers as long as necessary (1, 3, 2, 6, 4, 5, 1, 3, 2, 6, 4, 5, ...), and adding the products (1×1 + 7×3 + 3×2 = 1 + 21 + 6 = 28). The original number is divisible by 7 if and only if ...

  4. Division (mathematics) - Wikipedia

    en.wikipedia.org/wiki/Division_(mathematics)

    Logarithm tables can be used to divide two numbers, by subtracting the two numbers' logarithms, then looking up the antilogarithm of the result. Division can be calculated with a slide rule by aligning the divisor on the C scale with the dividend on the D scale. The quotient can be found on the D scale where it is aligned with the left index on ...

  5. Cross-multiplication - Wikipedia

    en.wikipedia.org/wiki/Cross-multiplication

    We can reduce the fractions to lowest terms by noting that the two occurrences of b on the left-hand side cancel, as do the two occurrences of d on the right-hand side, leaving =, and we can divide both sides of the equation by any of the elements—in this case we will use d —getting =.

  6. Divisor - Wikipedia

    en.wikipedia.org/wiki/Divisor

    For example, there are six divisors of 4; they are 1, 2, 4, −1, −2, and −4, but only the positive ones (1, 2, and 4) would usually be mentioned. 1 and −1 divide (are divisors of) every integer. Every integer (and its negation) is a divisor of itself. Integers divisible by 2 are called even, and integers not divisible by 2 are called odd ...

  7. Fraction - Wikipedia

    en.wikipedia.org/wiki/Fraction

    Unit fractions can also be expressed using negative exponents, as in 21, which represents 1/2, and 22, which represents 1/(2 2) or 1/4. A dyadic fraction is a common fraction in which the denominator is a power of two, e.g. ⁠ 1 / 8 ⁠ = ⁠ 1 / 2 3 ⁠. In Unicode, precomposed fraction characters are in the Number Forms block.

  8. Eisenstein's criterion - Wikipedia

    en.wikipedia.org/wiki/Eisenstein's_criterion

    Consider the polynomial Q(x) = 3x 4 + 15x 2 + 10.In order for Eisenstein's criterion to apply for a prime number p it must divide both non-leading coefficients 15 and 10, which means only p = 5 could work, and indeed it does since 5 does not divide the leading coefficient 3, and its square 25 does not divide the constant coefficient 10.

  9. Proof of Bertrand's postulate - Wikipedia

    en.wikipedia.org/wiki/Proof_of_Bertrand's_postulate

    Assume that there is a counterexample: an integer n ≥ 2 such that there is no prime p with n < p < 2n. If 2 ≤ n < 427, then p can be chosen from among the prime numbers 3, 5, 7, 13, 23, 43, 83, 163, 317, 631 (each being the largest prime less than twice its predecessor) such that n < p < 2n. Therefore, n ≥ 427.