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I am experimenting with simple differential geometry problem, computing the Frenet apparatus. 

beta = {-(4/5) Sin[s], -Cos[s], (3/5) Sin[s]}
{-((4 Sin[s])/5), -Cos[s], (3 Sin[s])/5}
myT = D[beta, s]
{-((4 Cos[s])/5), Sin[s], (3 Cos[s])/5}
kappa = Norm[D[myT, s]]
Sqrt[Abs[Cos[s]]^2 + Abs[Sin[s]]^2]

Obviously, kappa=1. How can I get Mathematica to recognize this fact?

Gene Naden
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    Simplify[kappa, Element[s, Reals]]? – kglr Jul 16 '18 at 06:07
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    You could also say Resolve[ForAll[s, kappa == 1], Reals] – kirma Jul 16 '18 at 07:16
  • Maybe your wording needs clarification, because it's not entirely clear what you mean by "Mathematica recognizing this fact." If you want a simplified form of kappa, use @kglr's Simplify, if you want to test if this assumption holds, use Resolve with ForAll as I commented above. – kirma Jul 16 '18 at 08:01

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