例1把如图方波信号进行分解 0<t< t 2 U <t<T T/2 T 解: 7(2\[at+()d=0 2 T T TJO 2 an= f(t)cos na, tdt U cos no,tdt To TJO T U cos no,tdt=0例1 把如图方波信号进行分解 t T/ 2 T U U u1 0 2 ( ) 2 T U t t T U t T u     =   −    解： 2 0 0 0 2 2 2 ( ) d ( )d 0 T T T T a f t dt U t U t T T   = = + − =          2 1 1 0 0 1 2 2 2 ( ) cos d cos d cos d 0 T T T T n f t n t t U n t t T T U n t t a    = = − =   