In geometry, when a cone and a plane intersect, a conic section results. There are three different types of sections, the parabola, the hyperbola and the ellipse. The circle is a special case of an ellipse. Sometimes the circle is mentioned as a fourth type, because calculating with a circle is easier than with an ellipse, most of the time. The conic sections are known at least since 200 BC, when Apollonius of Perga studied of their properties.