Unit Step Function Homework: Solve f(t) for t = -1

[jesuslovesu]

Homework Statement

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

Homework Equations

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?

 

[G01]

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.