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2010 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)