f(x)= [0 ] [2pi ] xf(cosx)dx put x=2pi-x in yhis integration. f(2pi-x)= 0 ] [2pi ] (2pi-x)f(cos(2pi-x))dx=2pi 0 [2pi ]f(cosx)dx- 0 ] [2pi ] xf(cosx)dx f(x)=f(2pi-x)=2pi 0 [2pi ]f(cosx)dx-f(x) 2f(x)=2pi 0 [2pi ]f(cosx)dx= f(x)= 0 [2pi ]f(cosx)dx=2 0 [pi ]f(cosx)dx=
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