2求y(t)=? cost x,(t) y x2(t) y(t) H1(j0) cos 1Ot cos 100t H1(0) 20. 20 20 100 100 解:x()= cost cos l0*.求y(t)=? cost  ( ) 1 x t ( ) H1 j  ( ) 1 y t cos10t ( ) H2 j cos100t ( ) 2 x t y(t) ( ) H1 j 20 − 20 20  ( ) H2 j  −100 100 1 x (t) cost cos10t 解： 1 =