SolutionSolution by Sequoia · ENThe function f :x⟼x8sin(x)f\colon x\longmapsto x^8\sin(x)f:x⟼x8sin(x) is odd since x⟼sin(x)x\longmapsto\sin(x)x⟼sin(x) is odd and x⟼x8x\longmapsto x^8x⟼x8 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=-II:=∫−ππf(x)dx=u=−x∫π−πf(−u)(−du)=∫−ππ(−f(u))du=−ISo I=0I=0I=0.
No messages yet.