Engineering Signals in discrete form (scaling, shifting etc.)

[jisbon]

Homework Statement

Given that x[n] = [5 1 7 9 4 3], where 5 is x[0].
Find x[n-1] , 2x[n-1] and -2x[n-1]+3

Relevant Equations

-

Attempting this question without any guidance from my professors unfortunately as they did not teach this bit. Searched online and also there aren't many questions like this.
From what I know,
(I) Having n-1 means you should shift right by 1, which means x[0] is now equals to 0? So x[n-1] = [0 5 1 7 9 4 3]?

ii) 2x[n-1] is simply a magnitude scaling of part one, so is it simply just 2x[n-1] = [0 10 2 14 18 8 6]?

(iii) -2x[n-1]+3. Is this simply again a magnitude scaling by -2 of part 1? Not sure how to do the +3 function though. Any help will be appreciated here :)

 

[Jody]

Do you know if x[n] is periodic?

Also which class is this for and what are some topics you just recently covered in class, or maybe which book are you following? If the problem came from the textbook, then what's the name of the chapter it's coming from? I'm trying to get more context.

 

[jisbon]

Do you know if x[n] is periodic?

Also which class is this for and what are some topics you just recently covered in class, or maybe which book are you following? If the problem came from the textbook, then what's the name of the chapter it's coming from? I'm trying to get more context.

I'm not sure, it wasn't stated. Digitial signal processing, and the question came from a worksheet, not a textbook.

 

[DaveE]

(I) Having n-1 means you should shift right by 1, which means x[0] is now equals to 0? So x[n-1] = [0 5 1 7 9 4 3]?

Well, that's as good an answer as any. But they didn't really tell you how to deal with x[0], did they? Some poorly defined questions have no answer. OTOH, I like your guess (which we call "zero padding" in the engineering world). You might also drop the 3 at the end, since in your answer you've increased the dimension of the vector, which is sometimes ok, and sometimes not. IDK.

Homework Statement:: Given that x[n] = [5 1 7 9 4 3], where 5 is x[0].
Find x[n-1] , 2x[n-1] and -2x[n-1]+3
Relevant Equations:: -

Not sure how to do the +3 function though.

Well they're asking you to add a vector to a scalar, in my interpretation. Again, undefined. But I like your approach of doing it element by element, nothing else makes much sense to me.

Sometimes the questions asked depend on the material previously presented; i.e. they are assuming that you will do things the way they showed you previously. Other times the instructors are lazy or idiots and they ask poorly worded questions. Writing good HW/test questions is often harder than it appears.