Monday, 13 January 2014

analysis - How can I obtain this division's limit without using derivatives?



limy0ycos(π2(1+y))


Can anybody help me? I can use basic properties of limits, and some of those basic known limits. I know it would be easier with derivatives, but I was just wondering if it's possible without L-Hospital's rule, derivatives, Taylor series.



Thank you in advance!



My ideas for now:

changing cosine into sine.
Maybe that. I have no other clue.


Answer



Note that limy0ycos(π2(1+y))=limy0ycos(π2+πy2)=limy0ysin(πy2)=2πlimy0(πy2)sin(πy2)=2π(1)=2π


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