

$$2p = 2a+2b$$
Perimeter
$$A = a \times b$$
Area
$$a = \frac{A}{b}$$
Length
$$b = \frac{A}{a}$$
Width
$$d = \sqrt{{a}^{2} + {b}^{2}}$$
Diagonal (Pythagoras' theorem)
$$a = \sqrt{{d}^{2}  {b}^{2}}$$
Length
$$b = \sqrt{{d}^{2}  {a}^{2}}$$
Width
Definition
A rectangle is a quadrilateral with internal angles congruent (right angles) and opposite sides congruent
Properties
 One side is larger (length) and the other smaller (width). The opposite sides are congruent (the sides are congruent in group of two)
 The sides can be also written as base (length) and height (width)
 Four congruent right angles
Data  Formula 

Perimeter  2p = 2 × a + 2 × b 
Area  A = a × b 
Diagonal  d = √( a^{2} + b^{2} ) 
Length  a = A / b 
Width  b = A / a 
Length  a = √( d^{2}  b^{2} ) 
Width  b = √( d^{2}  a^{2} ) 