Squaring the circle the circular arc b around O with radius , it results S'. Bisect the line segment in D and draw the semicircle b over D. Draw a straight line from O through C up to the semicircle b, it cuts b in E. The line segment is the mean proportional between and , also called geometric mean. Extend the line segment beyond O and transfer twice more, it results F and A, and thus the length of the line segment with the above described approximation value of formula_3, the half circumference of the circle. Bisect the line segment in G
Distance from a point to a line formula_39 perpendicular to the line. The distance from the point to the line is then just the norm of that vector. This more general formula is not restricted to two dimensions. If the vector space is orthonormal and if the line ("l" ) goes through point A and has a direction vector formula_45, the distance between point P and line ("l") is where formula_47 is the cross product of the vectors formula_48 and formula_45 and where formula_50 is the vector norm of formula_45. Note that cross products only exist in dimensions 3 and 7. Distance from a point to a