=z2(x=2 2 xX=-丌 0 3 no f(x)cos node=jk r cos nr 元 元 0 (-1)”-2(m=1,2,) f(x)的傅立叶展开式为 f(x)=+4(-1)2 2 2 cost(-∞<x<+) n=I n 上一页下一页返回=    0 ( )cos 2 an f x nxdx=    0 2 cos 2 x nxdx =    0 0 ( ) 2 a f x dx 2 0 2 3 2 2    =  x dx = ( 1,2, ) 4 ( 1) = − 2 n =  n n f (x) 的傅立叶展开式为   = −    +  − = + 1 2 2 cos ( ) ( 1) 4 3 ( ) n n nx x n f x 