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  2. Triangular number - Wikipedia

    en.wikipedia.org/wiki/Triangular_number

    A triangular number or triangle number counts objects arranged in an equilateral triangle. Triangular numbers are a type of figurate number , other examples being square numbers and cube numbers . The n th triangular number is the number of dots in the triangular arrangement with n dots on each side, and is equal to the sum of the n natural ...

  3. Law of sines - Wikipedia

    en.wikipedia.org/wiki/Law_of_sines

    In trigonometry, the law of sines, sine law, sine formula, or sine rule is an equation relating the lengths of the sides of any triangle to the sines of its angles. According to the law, ⁡ = ⁡ = ⁡ =, where a, b, and c are the lengths of the sides of a triangle, and α, β, and γ are the opposite angles (see figure 2), while R is the radius of the triangle's circumcircle.

  4. Heron's formula - Wikipedia

    en.wikipedia.org/wiki/Heron's_formula

    In this example, the triangle's side lengths and area are integers, making it a Heronian triangle. However, Heron's formula works equally well when the side lengths are real numbers. As long as they obey the strict triangle inequality, they define a triangle in the Euclidean plane whose area is a positive real number.

  5. Law of cosines - Wikipedia

    en.wikipedia.org/wiki/Law_of_cosines

    the third side of a triangle if two sides and an angle opposite to one of them is known (this side can also be found by two applications of the law of sines): [a] = ⁡ ⁡. These formulas produce high round-off errors in floating point calculations if the triangle is very acute, i.e., if c is small relative to a and b or γ is small compared to 1.

  6. Ordinal number - Wikipedia

    en.wikipedia.org/wiki/Ordinal_number

    In set theory, an ordinal number, or ordinal, is a generalization of ordinal numerals (first, second, n th, etc.) aimed to extend enumeration to infinite sets. [ 1 ] A finite set can be enumerated by successively labeling each element with the least natural number that has not been previously used.

  7. Centered triangular number - Wikipedia

    en.wikipedia.org/wiki/Centered_triangular_number

    The n-th centered triangular number, corresponding to n layers plus the center, is given by the formula:, = + (+) = + +. Each centered triangular number has a remainder of 1 when divided by 3, and the quotient (if positive) is the previous regular triangular number.

  8. Mollweide's formula - Wikipedia

    en.wikipedia.org/wiki/Mollweide's_formula

    In trigonometry, Mollweide's formula is a pair of relationships between sides and angles in a triangle. [1] [2] A variant in more geometrical style was first published by Isaac Newton in 1707 and then by Friedrich Wilhelm von Oppel in 1746. Thomas Simpson published the now-standard expression in 1748.

  9. Glossary of mathematical symbols - Wikipedia

    en.wikipedia.org/wiki/Glossary_of_mathematical...

    A mathematical symbol is a figure or a combination of figures that is used to represent a mathematical object, an action on mathematical objects, a relation between mathematical objects, or for structuring the other symbols that occur in a formula.