S=π (pi) ×a×b (where A and B are the lengths of the major axis and minor axis of the ellipse respectively) or S=π (pi) ×A×B/4 (where A and B are the lengths of the major axis and minor axis of the ellipse respectively).
Let the ellipse x_/a_+y_/b_= 1 take the area of the first quadrant, and y_=b_-b_/a_*x_ means y=√(b_-b_/a_*x_).
Since the inverse derivative of this formula is the required area, it is observed that the original formula is a circular equation formula *a/b, and according to (af(x))'=a*f'(x), when x=a, the circular area is a_π/4.