July 12, 2000 - Animation with Math.cos() | WebReference

# July 12, 2000 - Animation with Math.cos()

 July 12, 2000Animation with Math.cos() Tips: July 2000 Yehuda Shiran, Ph.D.Doc JavaScript
JavaScript supports the important trigonometric methods: `cos()`, `acos()`, `sin()`, `asin()`, `tang()`, `atan()`, and `atan2()`. All angles in JavaScript are measured in radians. You should know how to convert an angle from degrees to radians and vice versa. Check your conversion with the following table:

 Degrees Radians 0 0 90 0.5*PI 180 PI 270 1.5*PI 360 2*PI
where PI is the mathematical constant equal to 3.14... and 360 degrees are equal to 6.28... This tip covers the two cosine-related methods.

## cos()

The `Math.cos()` method accepts one argument (an angle in radians) and returns its cosine value. The following statement prints "-1":

``document.write(Math.cos(Math.PI));``

The `Math.cos()` method is useful in animation applications. If an object A revolves around object B in a constant-radius orbit, its y location can be derived by multiplying the orbiting radius by the cosine of the angle that the radius makes with the upright ray.

## acos()

The `Math.acos()` method accepts one argument and returns the arc cosine (the angle that the given number is its cosine value) of the argument, in radians. The following statement prints the value of PI:

``document.write(Math.acos(-1));``