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

A rectangle has a circumcircle with circumradius

but incircle only in the degenerate case of a square.

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

definition circle.

A circle is the set of points equidistant from a point C(h,k) called the
center. The fixed distance r from the center to any point on the circle is
called the radius.
The standard equation of a circle with center C(h,k) and radius r is as follows.

Reference.
http://www.analyzemath.com/CircleEq/Tutorials.html