The smallest positive real whose cosine is one is two times the smallest positive real whose sine is zero. Proved from axioms of IZF set theory via constructing reals, convergence and notation for infinite series, the exponential function, continuity, and the monotone intermediate value theorem. https://us.metamath.org/ileuni/taupi.html #PiDay #HalfTauDay #HalfTau #constructiveMathematics
