Question

I have a problem with Math.sin. I thought it would output the sinus of the given integer. So I tried Math.sin(30) and my output was -0.9880316240928618 and then I checked with my calculator and it was 0.5.

Answer 1

Parameters are assumed to be in radians, not degrees.

Try

Math.sin(Math.PI * (30/180));

A comment below notes that pre-computing the ratio π/180 is a good idea. One could add a companion to Math.sin that works on degrees this way:

Math.dsin = function() {
  var piRatio = Math.PI / 180;
  return function dsin(degrees) {
    return Math.sin(degrees * piRatio);
  };
}();

(Some people don’t like extending built-in objects, but since one doesn’t instantiate Math instances — at least, I don’t — this doesn’t seem terribly offensive.)