2-15 已知 _(1)(t)=u(t+1)-u(t-1) _(2)(t)=8(t+5)+8(t-5) _(3)(t)=-|||-(t+dfrac (1)(2))+s(t-dfrac (1)(2)) ,画出下列各卷积波形。-|||-(1) _(1)(t)=(f)_(1)(t)*(f)_(2)(t)-|||-(2) _(2)(t)=(f)_(1)(t)*(f)_(2)(t)*(f)_(2)(t)-|||-(3) _(3)(t)= [ {f)_(1)(t)+(f)_(2)(t))[ |x(t+5)-a(t-5)] } +(f)_(2)(t)-|||-(4) _(4)(t)=(f)_(1)(t)({f)_(3)}^2(t)