Formulas and Tables

Elementary Geometry


Side of a square: \(a\)
Diagonal of a square: \(d\)
Radius of the circumscribed circle: \(R\)
Radius of the inscribed circle: \(r\)

Perimeter: \(P\)
Area: \(S\)

  1. A square is a regular quadrilateral. It has four equal sides and four equal angles (\(90^\circ\) angles).
  1. Diagonal of a square
    \(d = a\sqrt 2\)
  2. Radius of the circumscribed circle
    \(R = d/2 =\) \(a\sqrt 2/2\)
  3. Radius of the inscribed circle
    \(r = a/2\)
  4. Perimeter of a square
    \(P = 4a\)
  5. Area of a square
    \(S = {a^2} = {\large\frac{{{d^2}}}{2}\normalsize} =\) \( 2{R^2} = 4{r^2}\)