# llAcos

 LSL Portal
Function: float llAcos( float val );
 172 Function ID 0 Forced Delay 10 Energy

Returns a float that is the arccosine in radians of val

 • float val – must fall in the range [-1.0, 1.0]

The returned value is in the range [0.0, PI][1], or NaN signifying a complex result when the parameter is out of range.

## Caveats

• Triggers a Math Error for complex results if not compiled in Mono.
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## Examples

```//  This example exercises the full valid range of argument from -1.0 to +1.0

default
{
touch_start(integer num_detected)
{
float random = llFrand(2.0) - 1.0;

llOwnerSay("The arccosine of " + (string)random + " is " + (string)llAcos(random));
}
}
```
```//An example for the Law of Cosines to calculate any angle of a triangle from 3 known side lengths.

default
{
touch_start(integer num_detected)
{
vector t=< llFrand(9.0)+1.0 , llFrand(9.0)+1.0 , llFrand(9.0)+1.0 >; //the 3 values of this vector are used to set the lengths of 3 sides of a triangle.

float anglexy=llAcos( (t.x*t.x+t.y*t.y-(t.z*t.z)) / ( 2*t.x*t.y) ) //Law Of Cosines

llOwnerSay("Using the Law Of Cosines, the angle of a triangle between side a="+(string)t.x+"and side b="+(string)t.y+"is = "+(string)anglexy+" radians="+(string)(anglexy*RAD_TO_DEG)+"° and that angle is not on side c="+(string)t.z);
}
}
```

### Functions

 • llSin llAsin – sine & inverse Sine • llCos – cosine • llTan llAtan2 – tangent & inverse tangent

## Deep Notes

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#### Footnotes

1. ^ The ranges in this article are written in Interval Notation.

#### Signature

```function float llAcos( float val );
```