Monday, July 4, 2016

trigonometry - Which is greater, cos(cos(1)) or cos(cos(cos(1)))?




What is the simplest way we can find which one of cos(cos(1)) and cos(cos(cos(1))) [in radians] is greater without using a calculator [pen and paper approach]? I thought of using some inequality relating cos(x) and x, but do not know anything helpful.
We can use basic calculus. Please help.


Answer



Since 0cos(x)1 for all 0xπ/2, and cos is a decreasing function on that region, you have 0cos(1)10cos(1)cos(cos(1))10cos(cos(cos(1)))cos(cos(1))1.


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