Tuesday, 15 July 2014

real analysis - on a limit exercise without using l'Hôpital's rule.




My professor gave us a number of limit exercises to solve without using l'Hôpital's rule, there is one that I am having problems with. I think I may of grouped it incorrectly in the ones where we were not allowed to use L'Hôpital.



The limit is the following:



limx2(sin(πx/2))3log(1+1/x)log(x23x+3x1)(exe2)



Is it possible to solve this without L'Hôpital?


Answer



Hint: limx2(sin(πx/2))3log(1+1x)log(x23x+3x1)(exe2)=limx2log(1+1x)(log(x23x+3x1)log(2232+321)x2)1(sin(πx/2)sin(π2/2)x2)2(sin(πx/2))(exe2x2)1.

Recognize the definition of ddxlog(x23x+3x1)|x=2, ddxsin(πx/2)|x=2 and of ddxex|x=2.



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