With a single-layer perceptron, it's easy to find the equation of the "separating line" (I don't know the professional term), the line that separates between the 2 types of points, based on the perceptron's weights, after it was trained. How can I find similarly the equation of the curve (not a straight line) that separates between the 2 types of points, in a multi-layer perceptron?

thanks.