f()=4+4co0+2C020+… +B, sin ot+ B, sin 2ot+ =4+∑(40o+;sino) f(dt A B T2-T2T f(cos kotdtk=1,2 fsin kott k=1,2 闪四 西南交通大学西南交通大学 f (t) = A0 + A1 coswt + A2 cos 2wt +L + B1 sinwt + B2 sin 2wt +L A (A k t B k t) k k k cos w sin w 1 = 0 +å + ¥ = ( ) ( ) L L sin 1, 2 2 cos 1, 2 2 0 0 = = = = ò ò f t k tdt k T B f t k tdt k T A T k T k w w f ( )t dt T A T ò = 0 0 1