\bigg),\end{align*}$$ and there are similar (lengthier!) formulas for \(\cos(360/257)\) and \(\cos(360/65537)\) using just nested square roots. Why these denominators? You’ll have to ask our friends Fermat and Galois . "What is algebra exactly; is it those three-cornered things?" —J. M. Barrie Search: Recent Posts What Makes Ellipses… Ellipses? More Putting Predicaments