### Circle

A **circle** is the path of a point which must always be a given distance (the radius) from another point (the centre of the circle).

##### Explanation

The circle with radius *r* is given by the equation *x*^{2} + *y*^{2} = *r*^{2}.

##### The number pi

You describe the area of a circle by *A* = π*r*^{2}. Therefore, for the unit circle with radius *r* = 1, this area is the real constant π = 3,1415…. This is a transcendental number and thus has infinitely many decimal places. Yet the surface area is clearly bounded. This is just how nature works. There is only one word for it - **incomprehensible**.