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# Source file src/math/asin.go

## Documentation: math

```     1  // Copyright 2009 The Go Authors. All rights reserved.
2  // Use of this source code is governed by a BSD-style
4
5  package math
6
7  /*
8  	Floating-point arcsine and arccosine.
9
10  	They are implemented by computing the arctangent
11  	after appropriate range reduction.
12  */
13
14  // Asin returns the arcsine, in radians, of x.
15  //
16  // Special cases are:
17  //	Asin(±0) = ±0
18  //	Asin(x) = NaN if x < -1 or x > 1
19  func Asin(x float64) float64
20
21  func asin(x float64) float64 {
22  	if x == 0 {
23  		return x // special case
24  	}
25  	sign := false
26  	if x < 0 {
27  		x = -x
28  		sign = true
29  	}
30  	if x > 1 {
31  		return NaN() // special case
32  	}
33
34  	temp := Sqrt(1 - x*x)
35  	if x > 0.7 {
36  		temp = Pi/2 - satan(temp/x)
37  	} else {
38  		temp = satan(x / temp)
39  	}
40
41  	if sign {
42  		temp = -temp
43  	}
44  	return temp
45  }
46
47  // Acos returns the arccosine, in radians, of x.
48  //
49  // Special case is:
50  //	Acos(x) = NaN if x < -1 or x > 1
51  func Acos(x float64) float64
52
53  func acos(x float64) float64 {
54  	return Pi/2 - Asin(x)
55  }
56
```

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