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Trigonometry nest (Posted on 2005-08-12) Difficulty: 4 of 5
Which is greater, sin(cos(x)) or cos(sin(x))? Prove it!

  Submitted by Federico Kereki    
Rating: 3.8333 (6 votes)
Solution: (Hide)
cos(sin(x)) is always greater.

First, we only need to consider x in [-π,π] by periodicity. Second, because sin(cos(x)) and cos(sin(x)) are both even, we only need to consider x in [0,π].

If x is in [π/2,π], then sin(cos(x))≤ sin(0)=0 ≤cos(1) ≤cos(sin(x)). So now suppose 0<x<π/2, and suppose sin(cos(x))=cos(sin(x)). Let y=sin(x), z=cos(x), so that 0

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Puzzle AnswerK Sengupta2024-01-03 11:34:51
re: range?Josh706792005-08-16 15:16:31
range?Jud2005-08-16 13:12:04
SolutionSolutionBractals2005-08-13 15:39:24
re: what gradeLarry2005-08-13 05:28:06
what gradejeffrey2005-08-13 04:30:34
SolutionNo SubjectJosh706792005-08-12 23:06:44
only the answer - I cheated.pcbouhid2005-08-12 22:53:06
Some Thoughtsnote the category; Close to a proof.Larry2005-08-12 22:43:02
Some Thoughtsre: Thoughts - Yes, but...e.g.2005-08-12 20:29:38
ThoughtsViet2005-08-12 20:18:10
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