var example_expr = new Array('5x^3y + 15xy + 10x^2', 'x^2 + 4x + 4', 'x^2 - 4', '2x^4 - 16x^2 + 32');
	var i = Math.floor(Math.random() * example_expr.length);
	
	function example(){
		var form = document.getElementById('calcForm')
		form.expression.value = example_expr[i];
		i += 1;
		if (i >= example_expr.length)
			i = 0;
	}