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For other uses, see Sine (disambiguation).

Sine function | |

Basic features | |

Parity | odd |

Domain | (−∞,∞)^{[note 1]} |

Codomain | [−1,1]^{[note 1]} |

Period | 2π |

Specific values | |

At zero | 0 |

Maxima | ((2k + ½)π, 1) ^{[note 2]} |

Minima | ((2k − ½)π, −1) |

Specific features | |

Root | kπ |

Critical point | kπ − π/2 |

Inflection point | kπ |

Fixed point | 0 |

In mathematics, the **sine function** is a trigonometric function of an angle. The sine of an angle is defined in the context of a right triangle: for the specified angle, it is the ratio of the length of the side that is opposite that angle to (divided by) the length of the longest side of the triangle (i.e. the hypotenuse).

Trigonometric functions are commonly defined as ratios of two sides of a right triangle containing the angle, and can equivalently be defined as the lengths of various line segments from a unit circle. More modern definitions express them as infinite series or as solutions of certain differential equations, allowing their extension to arbitrary positive and negative values and even to complex numbers.

The sine function is commonly used to model periodic phenomena such as sound and light waves, the position and velocity of harmonic oscillators, sunlight intensity and day length, and average temperature variations throughout the year.

The function sine can be traced to the *jyā* and *koṭi-jyā* functions used in Gupta period Indian astronomy (*Aryabhatiya*, *Surya Siddhanta*), via translation from Sanskrit to Arabic and then from Arabic to Latin.^{[1]} The word "sine" comes from a Latin mistranslation of the Arabic *jiba*, which is a transliteration of the Sanskrit word for half the chord, *jya-ardha*.^{[2]}

- 1 Right-angled triangle definition
- 2 Relation to slope
- 3 Relation to the unit circle
- 4 Identities
- 5 Properties relating to the quadrants
- 6 Series definition
- 7 Continued fraction
- 8 Fixed point
- 9 Arc length
- 10 Law of sines
- 11 Values
- 12 Relationship to complex numbers
- 13 History
- 14 Software implementations
- 15 See also
- 16 References

For "opposite" and the "adjacent" side (**tangent**), etc.

To define the trigonometric functions for an acute angle *A*, start with any right triangle that contains the angle *A*. The three sides of the triangle are named as follows:

- The
*adjacent side*is the side that is in contact with (adjacent to) both the angle we are interested in (angle*A*) and the right angle, in this case side**b**. - The
*hypotenuse*is the side opposite the right angle, in this case side**h**. The hypotenuse is always the longest side of a right-angled triangle. - The
*opposite side*is the side opposite to the angle we are interested in (angle*A*), in this case side**a**.

In ordinary Euclidean geometry, according to the triangle postulate the inside angles of every triangle total 180° (π radians). Therefore, in a right-angled triangle, the two non-right angles total 90° (π/2 radians), so each of these angles must be greater than 0° and less than 90°. The following definition applies to such angles.

The angle *A* (having measure α) is the angle between the hypotenuse and the adjacent side.

The **sine** of an angle is the ratio of the length of the opposite side to the length of the hypotenuse. In our case

does not depend on the size of the particular right triangle chosen, as long as it contains the angle *A*, since all such triangles are similar.

Main article: Slope

The trigonometric functions can be defined in terms of the *rise*, *run*, and *slope* of a line segment relative to some horizontal line.

- When the length of the line segment is 1, sine takes an angle and tells the
*rise* - Sine takes an angle and tells the
*rise*per unit length of the line segment. *Rise*is equal to sin*θ*multiplied by the length of the line segment

In contrast, cosine is used for the telling the *run* from the angle; and tangent is used for telling the *slope* from the angle. Arctan is used for telling the angle from the *slope*.

The line segment is the equivalent of the hypotenuse in the right-triangle, and when it has a length of 1 it is also equivalent to the radius of the unit circle.

In trigonometry, a unit circle is the circle of radius one centered at the origin (0, 0) in the Cartesian coordinate system.

Let a line through the origin, making an angle of *θ* with the positive half of the *x*-axis, intersect the unit circle. The *x*- and *y*-coordinates of this point of intersection are equal to cos *θ* and sin *θ*, respectively. The point's distance from the origin is always 1.

Unlike the definitions with the right or left triangle or slope, the angle can be extended to the full set of real arguments by using the unit circle. This can also be achieved by requiring certain symmetries and that sine be a periodic function.

See also: List of trigonometric identities

Exact identities (using radians):

These apply for all values of .

The reciprocal of sine is cosecant, i.e. the reciprocal of sin(*A*) is csc(*A*), or cosec(*A*). Cosecant gives the ratio of the length of the hypotenuse to the length of the opposite side:

The inverse function of sine is arcsine (arcsin or asin) or inverse sine (sin^{−1}). As sine is non-injective, it is not an exact inverse function but a partial inverse function. For example, sin(0) = 0, but also sin(π) = 0, sin(2π) = 0 etc. It follows that the arcsine function is multivalued: arcsin(0) = 0, but also arcsin(0) = π, arcsin(0) = 2π, etc. When only one value is desired, the function may be restricted to its principal branch. With this restriction, for each *x* in the domain the expression arcsin(*x*) will evaluate only to a single value, called its principal value.

*k* is some integer:

Or in one equation:

Arcsin satisfies:

and

See also: List of integrals of trigonometric functions and Differentiation of trigonometric functions

For the sine function:

The derivative is:

The antiderivative is:

*C* denotes the constant of integration.

It is possible to express any trigonometric function in terms of any other (up to a plus or minus sign, or using the sign function).

Sine in terms of the other common trigonometric functions:

f θ | Using plus/minus (±) | Using sign function (sgn) | |||||
---|---|---|---|---|---|---|---|

f θ = | ± per Quadrant | f θ = | |||||

I | II | III | IV | ||||

cos | + | + | - | - | |||

+ | - | - | + | ||||

cot | + | + | - | - | |||

+ | - | - | + | ||||

tan | + | - | - | + | |||

+ | - | - | + | ||||

sec | + | - | + | - | |||

+ | - | - | + |

Note that for all equations which use plus/minus (±), the result is positive for angles in the first quadrant.

The basic relationship between the sine and the cosine can also be expressed as the Pythagorean trigonometric identity:

where sin^{2}*x* means (sin(*x*))^{2}.

Over the four quadrants of the sine function is as follows.

Quadrant | Degrees | Radians | Value | Sign | Monotony | Convexity |
---|---|---|---|---|---|---|

1st Quadrant | increasing | concave | ||||

2nd Quadrant | decreasing | concave | ||||

3rd Quadrant | decreasing | convex | ||||

4th Quadrant | increasing | convex |

Points between the quadrants. k is an integer.

Degrees | Radians 0 ≤ | Radians | sin x | Point type |
---|---|---|---|---|

0° | 0 | 0 | Root, Inflection | |

90° | 1 | Maxima | ||

180° | 0 | Root, Inflection | ||

270° | -1 | Minima |

For arguments outside those in the table, get the value using the fact the sine function has a period of 360° (or 2π rad): , or use . Or use and . For complement of sine, we have .

Using only geometry and properties of limits, it can be shown that the derivative of sine is cosine, and that the derivative of cosine is the negative of sine.

Using the reflection from the calculated geometric derivation of the sine is with the 4n + k-th derivative at the point 0:

This gives the following Taylor series expansion at x = 0. One can then use the theory of Taylor series to show that the following identities hold for all real numbers *x* (where x is the angle in radians) :^{[3]}

If *x* were expressed in degrees then the series would contain messy factors involving powers of π/180: if *x* is the number of degrees, the number of radians is *y* = π*x* /180, so

The series formulas for the sine and cosine are uniquely determined, up to the choice of unit for angles, by the requirements that

The radian is the unit that leads to the expansion with leading coefficient 1 for the sine and is determined by the additional requirement that

The coefficients for both the sine and cosine series may therefore be derived by substituting their expansions into the pythagorean and double angle identities, taking the leading coefficient for the sine to be 1, and matching the remaining coefficients.

In general, mathematically important relationships between the sine and cosine functions and the exponential function (see, for example, Euler's formula) are substantially simplified when angles are expressed in radians, rather than in degrees, grads or other units. Therefore, in most branches of mathematics beyond practical geometry, angles are generally assumed to be expressed in radians.

A similar series is Gregory's series for arctan, which is obtained by omitting the factorials in the denominator.

The sine function can also be represented as a generalized continued fraction:

The continued fraction representation expresses the real number values, both rational and irrational, of the sine function.

Zero is the only real fixed point of the sine function; in other words the only intersection of the sine function and the identity function is sin(0) = 0.

Strict formulae:

Imprecise formulae for sine curve length from 0 to *x*: ^{[4]}

Main article: Law of sines

The law of sines states that for an arbitrary triangle with sides *a*, *b*, and *c* and angles opposite those sides *A*, *B* and *C*:

This is equivalent to the equality of the first three expressions below:

where *R* is the triangle's circumradius.

It can be proven by dividing the triangle into two right ones and using the above definition of sine. The law of sines is useful for computing the lengths of the unknown sides in a triangle if two angles and one side are known. This is a common situation occurring in *triangulation*, a technique to determine unknown distances by measuring two angles and an accessible enclosed distance.

See also: Exact trigonometric constants

x (angle) | sin x | |||
---|---|---|---|---|

Degrees | Radians | Grads | Exact | Decimal |

0° | 0 | 0^{g} | 0 | 0 |

180° | 200^{g} | |||

15° | 16^{2}⁄_{3}^{g} | 0.258819045102521 | ||

165° | 183^{1}⁄_{3}^{g} | |||

30° | 33^{1}⁄_{3}^{g} | 0.5 | ||

150° | 166^{2}⁄_{3}^{g} | |||

45° | 50^{g} | 0.707106781186548 | ||

135° | 150^{g} | |||

60° | 66^{2}⁄_{3}^{g} | 0.866025403784439 | ||

120° | 133^{1}⁄_{3}^{g} | |||

75° | 83^{1}⁄_{3}^{g} | 0.965925826289068 | ||

105° | 116^{2}⁄_{3}^{g} | |||

90° | 100^{g} | 1 | 1 |

A memory aid (note it does not include 15° and 75°):

x in degrees | 0° | 30° | 45° | 60° | 90° |

x in radians | 0 | π/6 | π/4 | π/3 | π/2 |

90 degree increments:

x in degrees | 0° | 90° | 180° | 270° | 360° |

x in radians | 0 | π/2 | π | 3π/2 | 2π |

0 | 1 | 0 | -1 | 0 |

Other values not listed above:

For angles greater than 2π or less than −2π, simply continue to rotate around the circle; sine periodic function with period 2π:

for any angle θ and any integer *k*.

The primitive period (the *smallest* positive period) of sine is a full circle, i.e. 2π radians or 360 degrees.

Sine is used to determine the imaginary part of a complex number given in polar coordinates (r,φ):

the imaginary part is:

r and φ represent the magnitude and angle of the complex number respectively. *i* is the imaginary unit. *z* is a complex number.

Although dealing with complex numbers, sine's parameter in this usage is still a real number. Sine can also take a complex number as an argument.

The definition of the sine function for complex arguments *z*:

where *i*^{ 2} = −1, and sinh is hyperbolic sine. This is an entire function. Also, for purely real *x*,

For purely imaginary numbers:

It is also sometimes useful to express the complex sine function in terms of the real and imaginary parts of its argument:

Using the partial fraction expansion technique in Complex Analysis, one can find that the infinite series

both converge and are equal to .

Similarly we can find

Using product expansion technique, one can derive

*sin z* is found in the functional equation for the Gamma function,

which in turn is found in the functional equation for the Riemann zeta-function,

As a holomorphic function, *sin z* is a 2D solution of Laplace's equation:

real component | imaginary component | magnitude |

real component | imaginary component | magnitude |

Main article: History of trigonometric functions

While the early study of trigonometry can be traced to antiquity, the trigonometric functions as they are in use today were developed in the medieval period. The chord function was discovered by Hipparchus of Nicaea (180–125 BC) and Ptolemy of Roman Egypt (90–165 AD).

The function sine (and cosine) can be traced to the *jyā* and *koṭi-jyā* functions used in Gupta period Indian astronomy (*Aryabhatiya*, *Surya Siddhanta*), via translation from Sanskrit to Arabic and then from Arabic to Latin.^{[1]}

The first published use of the abbreviations 'sin', 'cos', and 'tan' is by the 16th century French mathematician Albert Girard; these were further promulgated by Euler (see below). The *Opus palatinum de triangulis* of Georg Joachim Rheticus, a student of Copernicus, was probably the first in Europe to define trigonometric functions directly in terms of right triangles instead of circles, with tables for all six trigonometric functions; this work was finished by Rheticus' student Valentin Otho in 1596.

In a paper published in 1682, Leibniz proved that sin *x* is not an algebraic function of *x*.^{[5]} Roger Cotes computed the derivative of sine in his *Harmonia Mensurarum* (1722).^{[6]} Leonhard Euler's *Introductio in analysin infinitorum* (1748) was mostly responsible for establishing the analytic treatment of trigonometric functions in Europe, also defining them as infinite series and presenting "Euler's formula", as well as the near-modern abbreviations *sin., cos., tang., cot., sec.,* and *cosec.*^{[7]}

Look up in Wiktionary, the free dictionary.sine |

Etymologically, the word *sine* derives from the Sanskrit word for chord, *jiva**(*jya* being its more popular synonym). This was transliterated in Arabic as *jiba* جــيــب, abbreviated *jb* جــــب . Since Arabic is written without short vowels, "jb" was interpreted as the word *jaib* جــيــب, which means "bosom", when the Arabic text was translated in the 12th century into Latin by Gerard of Cremona. The translator used the Latin equivalent for "bosom", *sinus* (which means "bosom" or "bay" or "fold"). ^{[8]}^{[9]} The English form *sine* was introduced in the 1590s.

See also: Lookup table#Computing sines

The sine function, along with other trigonometric functions, is widely available across programming languages and platforms. In computing, it is typically abbreviated to `sin`

.

Some CPU architectures have a built-in instruction for sine, including the Intel x87 FPUs since the 80387.

In programming languages, `sin`

is typically either a built-in function or found within the language's standard math library.

For example, the C standard library defines sine functions within math.h: `sin(double)`

, `sinf(float)`

, and `sinl(long double)`

. The parameter of each is a floating point value, specifying the angle in radians. Each function returns the same data type as it accepts. Many other trigonometric functions are also defined in math.h, such as for cosine, arc sine, and hyperbolic sine (sinh).

Similarly, Python, defines `math.sin(x)`

within the built-in `math`

module. Complex sine functions are also available within the `cmath`

module, e.g. `cmath.sin(z)`

. CPython's math functions call the C `math`

library, and use a double-precision floating-point format.

There is no standard algorithm for calculating sine. IEEE 754-2008, the most widely used standard for floating-point computation, does not address calculating trigonometric functions such as sine.^{[10]} Algorithms for calculating sine may be balanced for such constraints as speed, accuracy, portability, or range of input values accepted. This can lead to different results for different algorithms, especially for special circumstances such as very large inputs, e.g. `sin(10`

.^{22})

A once common programming optimization, used especially in 3D graphics, was to pre-calculate a table of sine values, for example one value per degree. This allowed results to be looked up from a table rather than being calculated in real time. With modern CPU architectures this method may offer no advantage.^{[citation needed]}

Wikimedia Commons has media related to .Sine function |

Trigonometry |
---|

Reference |

Laws and theorems |

Calculus |

- Aryabhata's sine table
- Bhaskara I's sine approximation formula
- Discrete sine transform
- Euler's formula
- Generalized trigonometry
- Hyperbolic function
- Law of sines
- List of periodic functions
- List of trigonometric identities
- Madhava series
- Madhava's sine table
- Optical sine theorem
- Polar sine — a generalization to vertex angles
- Proofs of trigonometric identities
- Sine and cosine transforms
- Sine quadrant
- Sine wave
- Sine–Gordon equation
- Sinusoidal model
- Trigonometric functions

- ^
^{a}^{b}Boyer, Carl B. (1991). A History of Mathematics (Second ed.). John Wiley & Sons, Inc.. ISBN 0-471-54397-7, p. 210. **^**Victor J Katx, A history of mathematics, p210, sidebar 6.1.**^**See Ahlfors, pages 43–44.**^**Genetic programming: imprecise length of sin(x) curve**^**Nicolás Bourbaki (1994).*Elements of the History of Mathematics*. Springer.**^**"Why the sine has a simple derivative", in*Historical Notes for Calculus Teachers*by V. Frederick Rickey**^**See Boyer (1991).**^**See Maor (1998), chapter 3, regarding the etymology.**^**Victor J Katx,*A history of mathematics*, p210, sidebar 6.1.**^**Grand Challenges of Informatics, Paul Zimmermann. September 20, 2006 – p. 14/31 [1]