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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!

See The Solution Submitted by Federico Kereki    
Rating: 3.8333 (6 votes)

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Thoughts | Comment 1 of 11
Well, my first thoughts were to consider the range of each function.

Both sin(x) and cos(x) are periodic with a range of [-1, 1].

sin(x) is monotonically increasing on the interval [-1, 1] for x, and so the range of sin(cos(x)) is [sin(-1), sin(1)] ~= [-0.841, 0.841]. Also the average value of this function is thus 0.

cos(x) on the interval [-1, 1] however has a max of 1 at x=0, and decreases to cos(1) ~= 0.540 at x = +/-1. So cos(sin(x)) has a range of [0.540, 1], and thus the average value is positive.

Based on these observations, I would say that cos(sin(x)) is greater than sin(cos(x)).


  Posted by Viet on 2005-08-12 20:18:10
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