画出下列信号的波形1）f(t)=tu(t);2)f(t)=t[u(t)-u(t-2)];3)f(t)=(t-1)u(t-1);4)f(t)=sint/t画出图形~

　　画出下列信号的波形1）f(t)=tu(t);2)f(t)=t[u(t)-u(t-2)];3)f(t)=(t-1)u(t-1);4)f(t)=sint/t

　　画出图形~