Ivan Shishkin, Rye (1878)

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Solution

Solution by Sequoia · EN

The function f ⁣:x⟼x8sin⁡(x)f\colon x\longmapsto x^8\sin(x) is odd since x⟼sin⁡(x)x\longmapsto\sin(x) is odd and x⟼x8x\longmapsto x^8 is even.
Hence:
I:=∫−ππf(x) dx=u=−x∫π−πf(−u) (−du)=∫−ππ(−f(u)) du=−II:=\int_{-\pi}^{\pi}f(x)\,\mathrm{d}x\overset{u=-x}{= }\int_{\pi}^{-\pi}f(-u)\,(-\mathrm{d}u)=\int_{-\pi}^{\pi}(-f(u))\,\mathrm{d}u=-ISo I=0I=0.

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