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  2. Inverse trigonometric functions - Wikipedia

    en.wikipedia.org/wiki/Inverse_trigonometric...

    The notations sin −1 (x), cos −1 (x), tan1 (x), etc., as introduced by John Herschel in 1813, [7] [8] are often used as well in English-language sources, [1] much more than the also established sin [−1] (x), cos [−1] (x), tan [−1] (x) – conventions consistent with the notation of an inverse function, that is useful (for example ...

  3. List of trigonometric identities - Wikipedia

    en.wikipedia.org/wiki/List_of_trigonometric...

    Subtracting ⁡ from both sides and dividing by 2 by two yields the power-reduction formula for sine: ⁡ = (⁡ ()). The half-angle formula for sine can be obtained by replacing θ {\displaystyle \theta } with θ / 2 {\displaystyle \theta /2} and taking the square-root of both sides: sin ⁡ ( θ / 2 ) = ± ( 1 − cos ⁡ θ ) / 2 ...

  4. Tan-1 - Wikipedia

    en.wikipedia.org/wiki/Tan-1

    Tan-1, TAN-1, tan-1, or tan1 may refer to: tan1 y = tan1 ( x ), sometimes interpreted as arctan( x ) or arctangent of x , the compositional inverse of the trigonometric function tangent (see below for ambiguity)

  5. Proofs of trigonometric identities - Wikipedia

    en.wikipedia.org/wiki/Proofs_of_trigonometric...

    Illustration of the sine and tangent inequalities. The figure at the right shows a sector of a circle with radius 1. The sector is θ/(2 π) of the whole circle, so its area is θ/2. We assume here that θ < π /2. = = = ⁡ = ⁡

  6. Small-angle approximation - Wikipedia

    en.wikipedia.org/wiki/Small-angle_approximation

    The quantity 206 265 ″ is approximately equal to the number of arcseconds in a circle (1 296 000 ″), divided by 2π, or, the number of arcseconds in 1 radian. The exact formula is = ⁡ (″) and the above approximation follows when tan X is replaced by X.

  7. Tangent half-angle formula - Wikipedia

    en.wikipedia.org/wiki/Tangent_half-angle_formula

    The angle between the horizontal line and the shown diagonal is ⁠ 1 / 2 ⁠ (a + b). This is a geometric way to prove the particular tangent half-angle formula that says tan1 / 2 ⁠ (a + b) = (sin a + sin b) / (cos a + cos b). The formulae sin ⁠ 1 / 2 ⁠ (a + b) and cos ⁠ 1 / 2 ⁠ (a + b) are the ratios of the actual distances to ...

  8. Trigonometric functions - Wikipedia

    en.wikipedia.org/wiki/Trigonometric_functions

    Basis of trigonometry: if two right triangles have equal acute angles, they are similar, so their corresponding side lengths are proportional.. In mathematics, the trigonometric functions (also called circular functions, angle functions or goniometric functions) [1] are real functions which relate an angle of a right-angled triangle to ratios of two side lengths.

  9. Inverse tangent integral - Wikipedia

    en.wikipedia.org/wiki/Inverse_tangent_integral

    The inverse tangent integral is defined by: ⁡ = ⁡ The arctangent is taken to be the principal branch; that is, − π /2 < arctan(t) < π /2 for all real t. [1]Its power series representation is