s(t)=sin(t)u(t)*u(t-1)=∫(-∞→+∞)sin(x)u(x)u(t-1-x)dx=∫(-∞→+∞)sin(x)u(x)u(t-1-x)dx=∫(0→t-1)sin(x)dx (t>1)=-cos(t-1)+1 (t>1)t≤0时，s(t)=0
