var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.moveTo(0,0);
var x = 10;
var y;
var i;
for (i = 0; i < 25; i++) {
ctx.lineTo((2*i+1)*x,200);
y = 200*(i+1)/(i+2);
ctx.lineTo(2*(i+1)*x,y);
}
ctx.stroke();