	formula_html += "x<sup>" + String(points_for_interpolation.length - i - 1) + "</sup> + ";
		}
	}
	interpolation_formula.innerHTML = formula_html;
}

function draw_canvas(canvas_name){
	var canvas = document.getElementById(canvas_name);
	var context = canvas.getContext("2d");
	context.font = "16px sans-serif";
	// background
	context.fillStyle="#eeeeee";
	context.fillRect(0, 0, w, h);


	var points = [];
	if(canvas_name == "approximation_canvas") {
		points = points_for_approximation;
	} else if(canvas_name