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Math.cos(theta)

Arguments

theta

An angle, in radians (not degrees), normally in the range of 0 to 2, although any angle will suffice, as cosine is a periodic function.

Returns

The cosine of theta (the result is in the range of -1.0 to 1.0).

Description

The cos( ) function returns the trigonometric cosine of an angle. In a right triangle, the cosine of an angle is the result of dividing the length of the side adjacent to the angle by the triangle's hypotenuse.

Usage

Note that cos( ) expects angles to be provided in radians, not degrees.

Example

trace (cos(0));               // Displays: 1.0
trace (cos(Math.PI));         // Displays: -1.0

The cos( ) function can be used along with sin( ) to calculate a point on a circle, which we use in the following example to move a movie clip in a circular path. Given the radius of a circle, r, and an angle, xxxthetaxxx, measured counterclockwise from the positive horizontal axis, a point's location is (r*cosxxxthetaxxx, r*sinxxxthetaxxx):

// Global Function: degreesToRadians()
// Converts degrees to radians. There are 2*pi radians per 360 degrees.
_global.degreesToRadians = function (degrees) {
  return (degrees/180) * Math.PI;
}
   
// Method: MovieClip.moveInCircle()
//   Desc: Starts moving the clip around a circular path.
// Params: radius       Radius of circle path.
//         x            Horizontal center of circular path.
//         y            Vertical center of circular path.
//         degPerFrame  Number of degrees to move per frame rendered.
MovieClip.prototype.moveInCircle = function (radius, x, y, degPerFrame) {
  var deg = 0;          // Angle of object in degrees, measured
                        // counterclockwise from the horizon (X-axis).
   
  // Assign a movement function to run once per frame.
  this.onEnterFrame = function () {
    // Increase the rotation angle by 5 degrees
    deg += degPerFrame;
   
    // Place the object. Note that Flash inverts the Y-axis of Cartesian
    // coordinates so we decrement y to obtain our new location.
    var rotAngRad= degreesToRadians(deg);
    this._x = x + Math.cos(rotAngRad) * radius;
    this._y = y - Math.sin(rotAngRad) * radius;
  }
}
   
// Usage:
ball_mc.moveInCircle(100, 200, 200, 5);

See Also

Math.acos( ), Math.PI, Math.sin( ), Math.tan( )

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