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Unit step function

  1. Mar 17, 2008 #1
    1. The problem statement, all variables and given/known data
    I'm having a bit of difficulty understanding the unit step function
    For example
    f(t) = 6u(-t) + 6u(t+1) - 3u(t+2)
    t = -1

    2. Relevant equations

    3. The attempt at a solution

    If t = -1 then the way I would do the problem is say that if u(t) returns a negative number or zero then it's zero
    6(1) + 6u(0) - 3(1) = 3
    However, the answer is 9 so I must be misinterpreting how the unit step function works. Can anyone explain to me how one would handle the unit step function in this situation?
  2. jcsd
  3. Mar 17, 2008 #2


    User Avatar
    Homework Helper
    Gold Member

    The unit step function, u(x) is 1 at x=0, not 0. This is your problem. Try evaluating you expression, taking this into account, and you should get 9 as your answer.
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