Equilateral triangle inscribed in a circle

JavaScript

var canvas = document.createElement('canvas');
var ctx = canvas.getContext('2d');
var diameter = canvas.width = canvas.height = 400;
var radius = diameter / 2;
var width = radius;
var height = width;
var PiBy180 = Math.PI / 180;
var deg2rad = function(deg) {
    return deg * PiBy180
};
var xMult = -Math.cos(deg2rad(60));
var yMult = Math.sin(deg2rad(60));

document.body.appendChild(canvas);

function centeredSquare(size){
    centeredRectangle(size, size);
}

function centeredRectangle(width, height) {
    ctx.strokeRect(-width, -height, width * 2, height * 2);
}

function centeredCircle(radius) {
    ctx.moveTo(radius, 0);
    ctx.arc(0, 0, radius, 0, deg2rad(360), false);
}

function centeredEquilateralTriangle(size) {
    ctx.moveTo(size, 0);
    ctx.lineTo(xMult * size, yMult * size);
    ctx.lineTo(xMult * size, -yMult * size);
    ctx.lineTo(size, 0);
}

function centeredPoly(size, sides) {
    var i = sides;
    for ( var i=0; i <= sides; i++ ) {
        var renderTo = i === 0 ? 'moveTo' : 'lineTo';
        var x = Math.sin( i * Math.PI * 2 / sides ) * size;
        var y = Math.cos( i * Math.PI * 2 / sides ) * size;
      ctx[ renderTo ]( x, y );
    }
}

// make more like a traditional grid
ctx.translate(canvas.width / 2, canvas.height / 2);

//centeredCircle(width);
//centeredCircle(width/2)
//centeredCircle(width/4)
//centeredEquilateralTriangle(width/4);
centeredPoly(width / 2, 5 );
centeredPoly(width / 3, 4 );
centeredPoly(width / 5, 3 );

// finish
ctx.stroke();