说明：   一、 利用MATLAB产生下列连续信号并作图 （1） x(t)=-2u(t-1),-1<t<5 x(t)=cos(100t)+cos(3000t),设-0.1<t<0.1
(one, Using MATLAB produce the following continuous signals and mapping (1) x (t) =- u (t-1)-1)