Mark M. answered 02/27/18
Tutor
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Retired Math prof with teaching and tutoring experience in trig.
tan(x/2) = (1 - cosx) / sinx
So, if tan(x/2) = cotx. then (1 - cosx) / sinx = cosx / sinx
Therefore, 1 - cosx = cosx
2cosx = 1
cosx = 1/2 x = π/3 or 5π/3