自动控制原理（双语教学）：3.8.1.15

Solution 3.8.1.15 Applying the Laplace transform, assuming zero initial conditions, yields s 3 Y (s)+7s 2 Y (s)+31sY (s)+25Y (s)=U(s);; or (s 3 +7s 2 +31s +25)Y (s)=U: Rearranging yields Y (s) U(s) = 1 s 3 +7s 2 +31s +25 : 1