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===== Function: llAcos =====

<code lsl2>
float llAcos(float arg)
</code>

Return the inverse cosine of the argument, in radians. The inverse cosine (also known as arccosine) is the angle whose cosine is the given argument.

===== Parameters =====

=== arg ===
Number whose inverse cosine is to be found.

===== Return value =====

$lty[Float] number with the angle in radians that is the inverse cosine of the argument.

===== Notes =====

  * The range of $prm[arg] must be between -1 and 1, because the cosine of any angle can't be outside that range.
  * The result is always between 0 and $lct[PI], or $nan if the argument is out of the valid range.

===== Short examples =====

<code lsl2>
float angle;
angle = llAcos(1); // Sets angle to 0, because the cosine of 0 is 1.
angle = llAcos(0); // Sets angle to PI_BY_TWO, because the cosine of PI/2 is 0.
angle = llAcos(-1); // Sets angle to PI, because the cosine of PI is -1.
angle = llAcos(0.31); // Sets angle to approximately 1.255603 (the cosine of that is 0.31)

angle = llAcos(2);  // Under Mono, sets angle to NaN (Not a Number),
                    // because there's no number whose cosine is 2.
                    // Crashes with a math error under LSO.
</code>

===== Complete examples =====

A $lty[rotation] can be expressed by an axis and an angle. This example illustrates how to use $fn[llAcos] to obtain the angle component of a rotation, assumed it's normalized (most LSL functions return normalized rotations). If the rotation is not guaranteed to be normalized, use $lfn[llRot2Angle] instead.

<file lsl2 llAcos-example.lsl>
default
{
    state_entry()
    {
        rotation rot = llGetLocalRot();
        llOwnerSay("The angle of rotation of this prim is " + (string)(2*llAcos(rot.s)) + " radians.");
    }
}
</file>

===== See also =====

  * $lfn[llCos] calculates the cosine of the argument.
  * $lfn[llAsin] calculates the inverse sine of the argument.
  * $lfn[llSin] calculates the sine of the argument.
  * $lfn[llAtan2] calculates the angle of a 2D vector.
  * $lfn[llTan] calculates the tangent of the argument.
  * Other $lfn[math/] functions.