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'''Sine''' (<math>\sin</math>) is a [[Trigonometry|trigonometric]] ratio. In a [[right triangle]] with an angle <math>\theta</math> , |
'''Sine''' (<math>\sin</math>) is a [[Trigonometry|trigonometric]] ratio. In a [[right triangle]] with an angle <math>\theta</math> , |
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− | :<math>\sin(\theta)=\frac{\ |
+ | :<math>\sin(\theta)=\frac{\text{opposite}}{\text{hypotenuse}}</math> |
<math>\text{Opposite}</math> is the side of the triangle facing(opposite to) angle <math>\theta</math> , and <math>\text{hypotenuse}</math> is the side opposite the [[right angle]]. |
<math>\text{Opposite}</math> is the side of the triangle facing(opposite to) angle <math>\theta</math> , and <math>\text{hypotenuse}</math> is the side opposite the [[right angle]]. |
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:<math>\sin(\theta)=\frac{e^{\theta i}-e^{-\theta i}}{2i}</math> |
:<math>\sin(\theta)=\frac{e^{\theta i}-e^{-\theta i}}{2i}</math> |
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+ | |||
+ | If desired, the sine function may be calculated as a direct summation series: |
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+ | |||
+ | :<math>\sin(\theta)=\sum_{k=0}^\infty\frac{(-1)^k x^{2k+1}}{(2k+1)!}</math> |
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The [[reciprocal]] of sine is [[cosecant]] (abbreviated as <math>\csc</math>), while its inverse is <math>\arcsin</math> or <math>\sin^{-1}</math> . Note that sine is not being raised to the [[exponentiation|power]] of -1; this is an [[inverse function]], not a reciprocal. |
The [[reciprocal]] of sine is [[cosecant]] (abbreviated as <math>\csc</math>), while its inverse is <math>\arcsin</math> or <math>\sin^{-1}</math> . Note that sine is not being raised to the [[exponentiation|power]] of -1; this is an [[inverse function]], not a reciprocal. |
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− | The [[derivative]] of <math>\sin(x)</math> is <math>\cos(x)</math> , while its [[antiderivative]] is <math>-\cos(x)</math> . |
+ | The [[derivative]] of <math>\sin(x)</math> is <math>\cos(x)</math> , while its [[antiderivative]] is <math>-\cos(x)</math> . The derivative of <math>\arcsin(x)</math> is <math>\frac{1}{\sqrt{1-x^2}}</math> |
+ | |||
+ | ===Trigonometric identities=== |
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+ | Sine and cosine can be converted between each other. |
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+ | :<math>\sin(x)=\cos(\frac{\pi}{2}-x)=\cos(x-\frac{\pi}{2})=- \cos(\frac{\pi}{2}+x)</math> |
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+ | :<math>\sin^2(x)+\cos^2(x) = 1</math> |
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+ | |||
+ | Addition of angles under sine: |
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+ | :<math>\begin{align}&\sin(a+b)=\sin(a)\cos(b)+\cos(a)\sin(b)\\ |
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+ | &\sin(2a)=2\sin(a)\cos(a)\end{align}</math> |
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+ | |||
+ | The sine of an imaginary number becomes a variant of a hyperbolic sine: |
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+ | :<math>\sin(\theta i)=i\sinh(\theta)</math> |
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+ | |||
+ | The square of sine: |
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+ | :<math>\sin^2(\theta)=\frac{1-\cos(2\theta)}{2}</math> |
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+ | |||
+ | ===Limits=== |
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+ | |||
+ | :<math>\lim_{x\to 0} \left(\frac{\sin (x)}{x}\right) = 1</math> |
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+ | |||
+ | ===Approximations=== |
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+ | For small values of <math>\theta</math>, there is an easy approximation: |
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+ | :<math>\sin \theta \approx \theta \mbox{ if } \theta < 0.5</math> |
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+ | |||
+ | ==See also== |
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+ | *[[Cosine]] |
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+ | *[[Cosecant]] |
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+ | *[[Hyperbolic sine]] |
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+ | *[[Law of sines]] |
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{{Trig-stub}} |
{{Trig-stub}} |
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[[Category:Trigonometric identities]] |
[[Category:Trigonometric identities]] |
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+ | [[Category:Trigonometry]] |
Revision as of 12:52, 29 May 2020
Sine () is a trigonometric ratio. In a right triangle with an angle ,
is the side of the triangle facing(opposite to) angle , and is the side opposite the right angle.
Properties
The sine of an angle is the y-coordinate of the point of intersection of said angle and a unit circle.
As a result of Euler's formula, the sine function can also be represented as
If desired, the sine function may be calculated as a direct summation series:
The reciprocal of sine is cosecant (abbreviated as ), while its inverse is or . Note that sine is not being raised to the power of -1; this is an inverse function, not a reciprocal.
The derivative of is , while its antiderivative is . The derivative of is
Trigonometric identities
Sine and cosine can be converted between each other.
Addition of angles under sine:
The sine of an imaginary number becomes a variant of a hyperbolic sine:
The square of sine:
Limits
Approximations
For small values of , there is an easy approximation:
See also
- Cosine
- Cosecant
- Hyperbolic sine
- Law of sines