k sin -xdx cos nT 2 nc 2k当n=135, nTC k 2k πv13 5πv ∫(x)=+—(sin。+sin+sin。+…) T 25 2 (-00<x<+∞;≠0,+2,4, x=2n时级数收敛于 2  =  2 0 2 sin 2 1 xdx n bn k (1− cos )  = n n k , 0 2,4,6, 1,3,5, 2      = = =    n n n k 当 当 ) 2 5 sin 5 1 2 3 sin 3 1 2 (sin 2 2 ( ) +  +  +    = + k k x x x f x (−  x  +; x  0,2,4, ) 2 2 k x = n时级数收敛于