[理工] [工數]-Laplace..

[mdpming (.....)]

1.

 3y(t) - 4y(t-1) + 2y(t-2) = t


using the Laplace transform if y(t) = 0 for t<0


解答這一步我不太懂


          0      , t < 2
y(t-2) =
          y(t-2) , t > 2


得


y(t-2) = u(t-2)y(t-2)


請問這面這要怎麼看出來..我不會看..


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