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 0≤cos(x)≤1 for all 0≤x≤π/2, and cos is a decreasing function on that region, you have 0≤cos(1)≤1⇒0≤cos(1)≤cos(cos(1))≤1⇒0≤cos(cos(cos(1)))≤cos(cos(1))≤1.
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