In a multi-sensor system, you are working to minimize the calibration error E(x, y), where x and y are calibration parameters. The calibration error is modeled as: E(x, y) = x2 7y2 - 2xy + 3x + 4y - 15. Determine the critical points and classify them as minima or maxima. How will minimizing this calibration error improve the accuracy of your sensor readings?