.moveTo(x_to_client(start_x), y_to_client(start_y));
            context.lineTo(client_x, client_y);
            context.strokeStyle="#557755";
            context.stroke();
            context.setLineDash([]);
            context.closePath();
        }else if(document.getElementById("button_3").disabled){
            var a11 = solver_1_eq_1[0];
            var a12 = solver_1_eq_1[1];
            var b1 = solver_1_eq_1[2];
            var a21 = solver_1_eq_2[0];
            var a22 = solver_1_eq_2[1];
     