function calculate() {
	var x1 = document.getElementById("x<sub>1</sub>").value;
	var x2 = document.getElementById("x<sub>2</sub>").value;
	var y1 = document.getElementById("y<sub>1</sub>").value;
	var y2 = document.getElementById("y<sub>2</sub>").value;
	var distance;
	if (x1 != "" && x2 != "" && y1 != "" && y2 != "") {
		x1 = parseFloat(x1);
		x2 = parseFloat(x2);
		y1 = parseFloat(y1);
		y2 = parseFloat(y2);
		distance = Math.sqrt((Math.pow(x2-x1,2))+(Math.pow(y2-y1,2)));
		document.getElementById("distance").innerHTML = "distance: " + distance;
	}
}