---

tt=input('ввести временной интервал tn<=t<=tk [tn tk]:');

u0=@(t)-1-t;
u1=@(t)(57-4*t-25*exp(-4*t))/32;
u2=@(t)3-t/4;

figure()
fplot(@(t)[u0(t) u1(t) u2(t)],tt)
grid on, legend('U0(t)','U1(t)','U2(t)'),xlabel('t'),ylabel('U(t)')