Circle a triangle whose base has the length of the circle's circumference and whose height equals the circle's radius, which comes to multiplied by the radius squared: Equivalently, denoting diameter by "d", that is, approximately 79% of the circumscribing square (whose side is of length "d"). The circle is the plane curve enclosing the maximum area for a given arc length. This relates the circle to a problem in the calculus of variations, namely the isoperimetric inequality. Equation of a circle<br> In an "x"–"y" Cartesian coordinate system, the circle with centre coordinates ("a", "b") and radius "r" is the set of
Mohr's circle points formula_117 on the Mohr circle and the centre of the circle. This double angle relation comes from the fact that the parametric equations for the Mohr circle are a function of formula_35. It can also be seen that the planes formula_80 and formula_81 in the material element around formula_7 of Figure 5 are separated by an angle formula_135, which in the Mohr circle is represented by a formula_136 angle (double the angle). The second approach involves the determination of a point on the Mohr circle called the "pole" or the "origin of planes". Any straight line drawn from the