Friday, 28 November 2014

integration - How prove this limntoinftyintfracpi20sinxndx=0

show that

limnπ20sinxndx=0



I have see this similar problem
limnπ20sinnxdx=0


poof:
ξ>0,0<δ<ξ/2,and there is N,such 0<sinnπ/2δ<ξ/π(nN)
then we have
π/20sinnxdx=(π/2δ0+π/2π/2δ)sinnxdx=I1+I2

then
|I1|(sinπ/2δ)n(π/2δ)<ξ/ππ/2=ξ/2


and
|I2|(π/2(π/2δ))=δ<ξ/2

and This problem have many other methods,



But for this limnπ20sinxndx=0


I can't prove it,Thank you

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