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  2. List of trigonometric identities - Wikipedia

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

    A formula for computing the trigonometric identities for the one-third angle exists, but it requires finding the zeroes of the cubic equation 4x 3 − 3x + d = 0, where is the value of the cosine function at the one-third angle and d is the known value of the cosine function at the full angle.

  3. Proofs of trigonometric identities - Wikipedia

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

    The area of triangle OCD is CD/2, or tan(θ)/2. Since triangle OAD lies completely inside the sector, which in turn lies completely inside triangle OCD , we have sin ⁡ θ < θ < tan ⁡ θ . {\displaystyle \sin \theta <\theta <\tan \theta .}

  4. Pythagorean trigonometric identity - Wikipedia

    en.wikipedia.org/wiki/Pythagorean_trigonometric...

    satisfying respectively y(0) = 0, y ′ (0) = 1 and y(0) = 1, y ′ (0) = 0. It follows from the theory of ordinary differential equations that the first solution, sine, has the second, cosine, as its derivative, and it follows from this that the derivative of cosine is the negative of the sine. The identity is equivalent to the assertion that ...

  5. Small-angle approximation - Wikipedia

    en.wikipedia.org/wiki/Small-angle_approximation

    The red section on the right, d, is the difference between the lengths of the hypotenuse, H, and the adjacent side, A.As is shown, H and A are almost the same length, meaning cos θ is close to 1 and ⁠ θ 2 / 2 ⁠ helps trim the red away.

  6. Sine and cosine - Wikipedia

    en.wikipedia.org/wiki/Sine_and_cosine

    sin(x) cos(x) Degrees Radians Gradians Turns Exact Decimal Exact Decimal 0° 0 0 g: 0 0 0 1 1 30° ⁠ 1 / 6 ⁠ π ⁠33 + 1 / 3 ⁠ g ⁠ 1 / 12 ⁠ ⁠ 1 / 20.5 0.8660 45° ⁠ 1 / 4 ⁠ π: 50 g ⁠ 1 / 80.7071 0.7071 60° ⁠ 1 / 3 ⁠ π ⁠66 + 2 / 3 ⁠ g ⁠ 1 / 6 ⁠

  7. Chebyshev polynomials - Wikipedia

    en.wikipedia.org/wiki/Chebyshev_polynomials

    The real part of the other side is a polynomial in cos x and sin x, in which all powers of sin x are even and thus replaceable through the identity cos 2 x + sin 2 x = 1. By the same reasoning, sin nx is the imaginary part of the polynomial, in which all powers of sin x are odd and thus, if one factor of sin x is factored out, the remaining ...

  8. Trigonometric functions - Wikipedia

    en.wikipedia.org/wiki/Trigonometric_functions

    The y-axis ordinates of A, B and D are sin θ, tan θ and csc θ, respectively, while the x-axis abscissas of A, C and E are cos θ, cot θ and sec θ, respectively. Signs of trigonometric functions in each quadrant. Mnemonics like "all students take calculus" indicates when sine, cosine, and tangent are positive from quadrants I to IV. [8]

  9. Trigonometric functions of matrices - Wikipedia

    en.wikipedia.org/wiki/Trigonometric_functions_of...

    The analog of the Pythagorean trigonometric identity holds: [2] sin 2 ⁡ X + cos 2 ⁡ X = I {\displaystyle \sin ^{2}X+\cos ^{2}X=I} If X is a diagonal matrix , sin X and cos X are also diagonal matrices with (sin X ) nn = sin( X nn ) and (cos X ) nn = cos( X nn ) , that is, they can be calculated by simply taking the sines or cosines of the ...