Edit in JSFiddle

var c = document.getElementById('c');
c.width = 200;
c.height = 200;
var ctx = c.getContext('2d');
ctx.translate(100, 100);

ctx.beginPath();

ctx.lineTo(Math.cos(0) * 90, Math.sin(0) * 90);
ctx.lineTo(
    Math.cos(Math.PI * 1 / 2) * 90,
    Math.sin(Math.PI * 1 / 2) * 90);
ctx.lineTo(
    Math.cos(Math.PI) * 90,
    Math.sin(Math.PI) * 90);
ctx.lineTo(
    Math.cos(Math.PI * 3 / 2) * 90,
    Math.sin(Math.PI * 3 / 2) * 90);
ctx.lineTo(
    Math.cos(Math.PI * 4 / 2) * 90,
    Math.sin(Math.PI * 4 / 2) * 90);
ctx.lineTo(Math.cos(0) * 90, Math.sin(0) * 90);
ctx.stroke();
<canvas id='c'></canvas>