Objects - JavaScript: Novice to Ninja - page 153

Trigonometric Functions
The Math object also has the standard trigonometric functions, which are very useful when
working with geometrical objects. All angles are measured in radians for these functions.
Note: Remind Me About Radians
Radians are a standard unit of angular measurement, equal to the angle of
the circle's center corresponding to the arc that subtends it.
The Math.sin() returns the sine of an angle:
> Math.sin(Math.PI/6); // this calculation contains
rounding errors,
↵ it should be 0.5
<< 0.49999999999999994
The Math.cos() returns the cosine of an angle:
> Math.cos(Math.PI/6);
<< 0.8660254037844387
The Math.tan() returns the tangent of an angle:
> Math.tan(Math.PI/4); // another rounding error, this
should be 1
<< 0.9999999999999999
> Math.tan(Math.PI/2); // this should be NaN or Infinity
<< 16331778728383844
The Math.asin() returns the arcsine of a number. The result is an angle:
> Math.asin(1);
<< 1.5707963267948966
The Math.acos() returns the arccosine of a number. The result is an angle: