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
Circle Line Downtown Circle Line Downtown Circle Line Downtown is a sightseeing harbor cruise company that operates out of the South Street Seaport Pavilion Pier at the Financial District in Manhattan under Harbor Experience Companies. Circle Line Downtown was established by President J.B. Meyer, third generation owner and operator of the family that founded the company and Circle Line Sightseeing Cruises brand. In 1953, Frank Barry, Gerald O'Driscoll, Helen Mitchell, William Moran, and Frank Clair founded Circle Line, the nautical sightseeing operation, providing cruises which circled Manhattan. The company's fleet was then a collection of modified craft, including surplus landing crafts from World