Geometry calculators

Which calculation do you need

Plane figures answer the two questions that always arrive together: how long is the outline and how much surface does it enclose. The triangle is solved from its three sides with Heron's formula, so the height is never needed; the regular polygon from the number of sides and the side length; the ellipse has an exact area but a perimeter that can only be approximated. Solids add the third dimension: besides volume and total surface you get the lateral surface — the figure that matters when you are painting the sides and not the ends — and the slant height of a cone or pyramid, the measurement problems usually hide. When the outline is not enough and the whole triangle is wanted, the triangle solver recovers it from any three measurements among the sides and angles — including the case where two triangles fit the data and both have to be shown. And when only a slice of a circle is wanted, the arc, chord, sagitta, sector and segment all follow from the radius plus one other measurement.