Greg's Handy formulas

handy.txt

Radians of a circle:  Math.PI * 2;
Radians to degrees:  radians * 180 / Math.PI;
Degrees to radians:  degrees * Math.PI / 180;
Midpoint interpolation: minValue + (maxValue - minValue) * percent
Angle (radians) between two points: Math.atan2(end.y-start.y, end.x-start.x)

distance between two points:  pythagorean theorem...

function distance(start, end) {
  var a = start.x-end.x, b = start.y-end.y;
  return Math.sqrt(a*a + b*b);
}

X-coordinate offset at angle: offset * Math.sin(angleRadians);
Y-coordinate offset at angle: offset * Math.cos(angleRadians);

Offset from origin at angle:

function radialOffset(origin, offset, angleRadians) {
  return {
    x: origin.x + offset * Math.sin(angleRadians),
    y: origin.y + offset * Math.cos(angleRadians)
  };
}