{{DISPLAYTITLE:_ASIN}}
The '''_ASIN''' function returns the angle measured in radians based on an input [[SIN]]e value ranging from -1 to 1.


{{PageSyntax}} 
::::: radian_angle! = _ASIN(''sine_value!'')


* The ''sine_value!'' must be measured &gt;= -1 and &lt;= 1, or else it will generate a return value of -1.#IND, which is basically QB64's way of telling us that the number doesn't exist. 
* ARCSINE is the inverse function of [[SIN]]e, and turns a [[SIN]]e value back into an angle.
* Note: Due to rounding with floating point math, the _ASIN may not always give a perfect match for the SIN angle which generated this.  You can reduce the number of rounding errors by increasing the precision of your calculations by using [[DOUBLE]] or [[_FLOAT]] precision variables instead of [[SINGLE]].

* ''(Only available in QB64-GL, from Dirty Builds after 06/20/2014.  Previous versions of QB64 don't support this command.)''


''Example:'' Converting a radian angle to its SINe and using that value to find the angle in degrees again using _ASIN:
{{CodeStart}} '' ''
{{Cl|DEFDBL}} A-Z

{{Cl|INPUT}} &quot;Give me an Angle (in Degrees) =&gt; &quot;; Angle
{{Cl|PRINT}}
C = {{Cl|SIN}}({{Cl|_D2R}}(Angle)) '_D2R is the command to convert Degrees to Radians, which is what SIN expects
{{Cl|PRINT}} &quot;The SINE of the Angle is: &quot;; C
A = {{Cl|_ASIN}}(C)
{{Cl|PRINT}} &quot;The ASIN of &quot;; C; &quot; is: &quot;; A
{{Cl|PRINT}} &quot;Notice, A is the Angle in Radians.  If we convert it to degrees, the value is &quot;; {{Cl|_R2D}}(A) '' ''
{{CodeEnd}}
{{small|Example by SMcNeill}}
{{OutputStart}}
Give me an Angle (in Degrees) =&gt; ? 60

The SINE of the Angle is:  .8660254037844386
The ACOS of   .8660254037844386  is:   1.047197551196598
Notice, A is the Angle in Radians.  If we convert it to degrees, we discover the value is  60
{{OutputEnd}}


''See also:''
* [[_D2G]] {{text|(degree to gradient}}, [[_D2R]] {{text|(degree to radian)}}
* [[_G2D]] {{text|(gradient to degree)}}, [[_G2R]] {{text|(gradient to degree}}
* [[_R2D]] {{text|(radian to degree)}}, [[_R2G]] {{text|(radian to gradient}}
* [[COS]] {{text|(cosine)}}, [[SIN]] {{text|(sine)}}, [[TAN]] {{text|(tangent)}}
* [[_ACOS]] {{text|(arc cosine)}}, [[_ASIN]] {{text|(arc sine)}}, [[ATN]] {{text|(arc tangent)}}
* [[_ACOSH]] {{text|(arc hyperbolic  cosine)}}, [[_ASINH]] {{text|(arc hyperbolic  sine)}}, [[_ATANH]] {{text|(arc hyperbolic  tangent)}}
* [[_ATAN2]] {{text|(Compute arc tangent with two parameters)}}
* [[_HYPOT]] {{text|(hypotenuse)}}
*[[Mathematical Operations]]
*[[Mathematical_Operations#Derived_Mathematical_Functions|Derived Mathematical Functions]]


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