T b,=o (x)sin ndx=5o'-xsinnxdx 2-x cos/x+ sin/xk ☆Dm=2(-1y,(m=12,) 210 A∫(x)=2(ix-,sin2x+sin3x-…) s2(1)+1 n-=1 (-∞<x<+∞;x≠土π,±3π,) 上圆  =  0 ( )sin 2 bn f x nxdx   =  0 sin 2 x nxdx  − +  = 2 0 ] cos sin [ 2 n nx n x nx = − n n cos 2 ( 1) , 2 +1 = − n n (n = 1,2, ) sin3 ) 3 1 sin2 2 1 f (x) = 2(sin x − x + x − sin . ( 1) 2 1 1   = + − = n n nx n (−  x  +; x  ,  3, )