# 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

$
p = q = \sqrt{(a{^2}+b{^2})}
$
A rectangle has a circumcircle with circumradius

$
R = (1 \div 2) \sqrt{(a{^2}+b{^2})}
$
but incircle only in the degenerate case of a square.

Reference :
http://mathworld.wolfram.com/Rectangle.html