rectangle +



A closed planar quadrilateral with opposite sides of equal lengths and ,
and with four right angles. A square is a degenerate rectangle with a=b

The area of the rectangle is A=ab

and its polygon diagonals p and q are of length
<br /> p = q = \sqrt{(a{^2}+b{^2})}<br />
A rectangle has a circumcircle with circumradius
<br /> R = (1 \div 2)  \sqrt{(a{^2}+b{^2})}<br />
but incircle only in the degenerate case of a square.
Reference :
http://mathworld.wolfram.com/Rectangle.html