show that
limn→∞∫π20sinxndx=0
I have see this similar problem
limn→∞∫π20sinnxdx=0
poof:
∀ξ>0,0<δ<ξ/2,and there is N,such 0<sinnπ/2−δ<ξ/π(n≥N)
then we have
∫π/20sinnxdx=(∫π/2−δ0+∫π/2π/2−δ)sinnxdx=I1+I2
then
|I1|≤(sinπ/2−δ)n(π/2−δ)<ξ/π⋅π/2=ξ/2
and
|I2|≤(π/2−(π/2−δ))=δ<ξ/2
and This problem have many other methods,
But for this limn→∞∫π20sinxndx=0
I can't prove it,Thank you
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