Using the intersecting chords theorem ( also known as power of a point or secant tangent theorem ) it is possible to calculate the radius " r " of a circle given the height " H " and the width " W " of an arc:
12.
The summation in the above expression is performed over all \ textstyle n-tuples of distinct points, including permutations, which can be contrasted with the definition of the multiplication while the existence of various point process notation means that the " n "-th factorial power of a point process is sometimes defined using other notation.
