令x=c,有 0 ∑ cos nc+ -sin nc 两式相减并整理,即得到 Sin nx- sin nc cos nx+ cos nc F(x) f(1)-0dt= 2 ∑|an +6 sin nt)d令 x = c ,有 = = + − + 1 0 cos sin 2 0 n n n nc n a nc n A b , 两式相减并整理,即得到 F(x) = 0 ( ) d 2 x c a f t t − = − + + − = 1 sin sin cos cos n n n n nx nc b n nx nc a 1 ( cos sin )d x n n c n a nt b nt t = = +