In geometry

Geometry

Geometry arose as the field of knowledge dealing with spatial relationships. Geometry was one of the two fields of pre-modern mathematics, the other being the study of numbers ....

, the Pitot theorem, named after the French engineer Henri Pitot

Henri Pitot

Henri Pitot was a French hydraulic engineer and the inventor of the Pitot tube.He became interested in studying the flow of water at various depths and was responsible for disproving the prevailing belief that speed of water increases with depth.In a Pitot tube the height of the fluid column is...

, states that in a tangential quadrilateral

Tangential quadrilateral

In Euclidean geometry, a tangential quadrilateral or circumscribed quadrilateral is a convex quadrilateral whose sides all lie tangent to a single circle inscribed within the quadrilateral. This circle is called the incircle...

 (i.e. one in which a circle

Circle

A circle is a simple shape of Euclidean geometry consisting of those points in a plane that are a given distance from a given point, the centre. The distance between any of the points and the centre is called the radius....

can be inscribed) the two sums of lengths of opposite sides are the same. The theorem is a consequence of the fact that two tangent line segments from a point outside the circle to the circle have equal lengths.