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acosArc cosine


float acos ( float $arg )

Returns the arc cosine of arg in radians. acos() is the complementary function of cos(), which means that a==cos(acos(a)) for every value of a that is within acos()' range.



The argument to process

Return Values

The arc cosine of arg in radians.

See Also

User Contributed Notes
anthony at interiorgoodsdirect dot com
05-Dec-2007 01:28
To calculate an angle from a triangle's sides.

Use the 'law of cosines' :

//        a_+b_-c_           
// cosC = --------
//           2ab

function calculateAngle($c,$a,$b)
$angleInRadians=acos((pow($a,2) + pow($b,2) - pow($c,2)) / (2 * $a * $b));

$a, $b, $c are the triangle sides.

The function returns the angle opposite side c, in degrees.
zoltan dot szentesi at nokia dot com
06-Aug-2006 10:29
Wondering what is the use of 'acos' function?

It is essential in games, animations and drawings to determine the location of two objects relating to each other.

To the point: the angle of two vectors is calculated by

           v1X*v2X + v1Y*v2Y
  acos(--------------------------)=angle between two vectors.
               |v1| * |v2|

 |v1| and |v2| are the length of the vectors and calculated using Pithagoras-formula: |v1|=sqrt(v1X*v1X + v1Y*v1Y)

This helped me to calculate and share given space for 'n' amount of objects so that they don't overlap.

Enjoy! :-)

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