IsWrittenThroughTheComplexNumbers​(AngouriMath.​Entity)

Whether a value is written through numbers that are not real: i, or a square root
of a negative number. Every angle here is real, so such a value is a real number whose
radical form needs the complex numbers, casus irreducibilis, and the function of its angle
is the shorter answer: cos(2pi/7) is
(-1 + cbrt((7 + 21 sqrt(-3))/2) + cbrt((7 - 21 sqrt(-3))/2))/6, and no real
radical form exists. sin(pi/7) simplified to the half-angle of it, many times
longer than the input. Such an entry is passed over rather than removed, so the closed form
stays on record. https://github.com/asc-community/AngouriMath/issues/2143