Tuesday, December 11, 2018

calculus - Evaluating limxrightarrowpifracsinxx2pi2 without L'Hopital


I need to calculate the following limit (without using L'Hopital - I haven't gotten to derivatives yet):


limxπsinxx2π2


We have sin function in the numerator so it looks like we should somehow make this similair to limx0sinxx. When choosing t=x2π2 we get limt0sint+π2t so it's almost there and from there I don't know what to do. How to proceed further? Or maybe I'm doing it the wrong way and it can't be done that way?


Answer



Choosing the substitution xπ=t, with t0, we have limxπsinxx2π2=limt0sin(t+π)t(t+2π)=limt0sintt(t+2π)=12π



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