Diameter of a circle × .7071 = Side of an inscribed square.
Circumference of a circle × .226 = Side of an inscribed square.
Circumference of a circle × .282 = Side of square of equal area.
Diameter of a circle × .8862 = Side of a square of equal area.
Base of a triangle × one-half the altitude = Area.
The product of both diameters × .7854 = Area of an ellipse.
Surface of a sphere × one-sixth of its diameter = Solidity.
Circumference of a sphere × its diameter = Surface.
Square of the circumference of a sphere × .3183 = Surface.