Suppose that there is an ellipse that meets with the square, but exactly inside the rhombus. The rhombus's side would be some $x$ cm. (for e.g., we can take it as $2 \ cm$.) The ellipse would have a major axis (with half being $a$) and minor axis (with half being $b$).
What would be the maximum area of the ellipse?
Edit: Rhombus can be freely shaped - it only has limitation of side $x \ cm$ thing.