Angle trisection with coefficients in the field generated by these numbers. Therefore, any number that is constructible by a sequence of steps is a root of a minimal polynomial whose degree is a power of two. Note also that radians (60 degrees, written 60°) is constructible. The argument below shows that it is impossible to construct a 20° angle. This implies that a 60° angle cannot be trisected, and thus that an arbitrary angle cannot be trisected. Denote the set of rational numbers by . If 60° could be trisected, the degree of a minimal polynomial of over would be a power
Triangle β is the interior angle at "B", formula_28 is the interior angle at "C" and "c" is the line AB). Furthermore, since sin α = sin ("π" − α) = sin (β + formula_28), and similarly for the other two angles: "Knowing AAS": and analogously if the known side is "a" or "c". "Knowing ASA": and analogously if the known side is "b" or "c". The shape of the triangle is determined by the lengths of the sides. Therefore, the area can also be derived from the lengths of the sides. By Heron's formula: where formula_34 is the semiperimeter, or