Calculate the area of a circle inscribed in a rectangle

Quickly calculate the area of ​​an inscribed circle

S=π(pi)×a×b (where a, b are the lengths of the major and minor semi-axes of the ellipse, respectively).   

Or S=π(pi)×A×B/4 (where A, B are the length of the long axis and the short axis of the ellipse, respectively).

The standard equation for an ellipse is x^2/a^2+y^2/b^2=1

The long axis of the long ellipse with a rectangle is equal to 2a, and the width = short axis is 2b

Ellipse area S=a*bπ

The area of ​​the rectangle A=2a*2b=4ab

The ratio of the areas of an ellipse to a rectangle is π: 4