# Quadrature of the circle

2020 Mathematics Subject Classification: *Primary:* 51M04 [MSN][ZBL]

The problem of constructing a square of equal area as the given circle; one of the classical Ancient problems on constructions with a ruler and compass. The side of a square equal in area to a circle of radius $r$ has length $r\sqrt\pi$. Thus the problem of the quadrature of the circle reduces to the following: To construct a line of length $\sqrt\pi$. Such a construction cannot be realized with a ruler and compass since $\pi$ is a transcendental number, as was proved in 1882 by F. Lindemann. However, the problem of the quadrature of a circle is solvable if one extends the means of construction, for example, by using certain transcendental curves, called quadratrices (cf. Quadratrix).

#### References

[1] | Yu.I. Manin, "Ueber die Lösbarkeit von Konstruktionsaufgaben mit Zirkel und Lineal" , Enzyklopaedie der Elementarmathematik , 4. Geometrie , Deutsch. Verlag Wissenschaft. (1969) pp. 205–230 (Translated from Russian) |

#### Comments

The Ancient problem of squaring the circle led to a problem in measure theory which asks if a disc and a square of equal area are equi-decomposable, i.e. if the disc can be decomposed into a finite number of disjoint subsets which can be reassembled to form a square, [a6]. Cf. Tarski problem for results on this problem.

#### References

[a1] | L. Bieberbach, "Theorie der geometrischen Konstruktionen" , Birkhäuser (1952) |

[a2] | F. Klein, et al., "Famous problems and other monographs" , Chelsea, reprint (1962) (Translated from German) |

[a3] | I. Stewart, "Galois theory" , Chapman & Hall (1973) pp. Chapt. 5 |

[a4] | B.L. van der Waerden, "Science awakening" , 1 , Noordhoff (1975) (Translated from Dutch) |

[a5] | U. Dudley, "A budget of trisections" , Springer (1987) |

[a6] | S. Wagon, "Circle squaring in the twentieth century" Math. Intelligencer , 3 : 4 (1981) pp. 176–181 |

[a7] | E.W. Hobson, "Squaring the circle" , Squaring the circle and other monographs , Chelsea, reprint (1953) |

[a8] | O. Perron, "Irrationalzahlen" , de Gruyter (1960) |

[a9] | W.W.R. Ball, H.S.M. Coxeter, "Mathematical recreations and essays" , Dover, reprint (1987) pp. 347–359 |

**How to Cite This Entry:**

Quadrature of the circle.

*Encyclopedia of Mathematics.*URL: http://encyclopediaofmath.org/index.php?title=Quadrature_of_the_circle&oldid=36963