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
Distance from a point to a line the same point and the line is |"ax" + "c"| / |"a"|, as measured along a horizontal line segment. If the line passes through two points "P"=("x","y") and "P"=("x","y") then the distance of (x,y) from the line is: The denominator of this expression is the distance between "P" and "P". The numerator is twice the area of the triangle with its vertices at the three points, (x,y), "P" and "P". See: . The expression is equivalent to formula_4, which can be obtained by rearranging the standard formula for the area of a triangle: formula_5, where "b" is the length of