Polar form?

Discussion in 'Math' started by Biggsy100, Jun 9, 2015.

  1. Biggsy100

    Thread Starter Member

    Apr 7, 2014
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    If A=1+j2 and B+2-J3, Find by calculation the magnitude and argument of the following complex numbers, stating each result in polar form:

    (i) A+B = (1+j2) + (2-j3)

    Is this where I cross multiply with first brackets and 2nd brackets....so 1 x 2 + 2 x6 2x2 +2 x 6 to get my answer

    I also have A - B , A x B , A/B
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    I don't think so.
    A + B = (1 + 2) + (j2 - j3) = 3 -j1
    You try A - B
     
  3. tjohnson

    Active Member

    Dec 23, 2014
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    Adding real and complex numbers together is like adding apples and oranges. Therefore, it is impossible to add terms such as 1 and j2 or 2 and -j3. However, you can add terms of the same sort together the way Papabravo showed.
     
  4. Biggsy100

    Thread Starter Member

    Apr 7, 2014
    88
    1
    ? Ok, so it's as simple as moving the j over?
     
  5. tjohnson

    Active Member

    Dec 23, 2014
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    Last edited: Jun 9, 2015
  6. WBahn

    Moderator

    Mar 31, 2012
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    This looks like homework. Is it. If so, it is better placed in the Homework Help forum where it will get more attention than in the Math forum. If it's homework, I can move it.
     
  7. Biggsy100

    Thread Starter Member

    Apr 7, 2014
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    This is a nightmare, that's what it is... :). It's actually an assignment that I missed on my course.
     
  8. WBahn

    Moderator

    Mar 31, 2012
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    What is the course? Are you supposed to just be learning about complex numbers, or are you supposed to already be familiar with them at this point? If the latter, then you will really need to look at some of those resources that have been linked in your various threads.
     
  9. Biggsy100

    Thread Starter Member

    Apr 7, 2014
    88
    1
  10. Biggsy100

    Thread Starter Member

    Apr 7, 2014
    88
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    (
    HND - Analytical methods for Engineers
     
  11. WBahn

    Moderator

    Mar 31, 2012
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    I have no idea what that course entails and what the prerequisites are. So is it assumed that you have never seen complex numbers before taking this course or not?
     
  12. Biggsy100

    Thread Starter Member

    Apr 7, 2014
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    You 'Assumed' right
     
  13. WBahn

    Moderator

    Mar 31, 2012
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    I didn't assume anything, I asked about what assumption the course makes regarding your prior knowledge of complex numbers. And since the question was duel ended (the "or not" at the end), it doesn't have a "yes" or "no" answer. So let me make it a yes or no question.

    Is this course taught based on the assumption that the students have never seen complex numbers before?
     
  14. Biggsy100

    Thread Starter Member

    Apr 7, 2014
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    not sure ...I am a student not a teacher!
     
  15. WBahn

    Moderator

    Mar 31, 2012
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    Here j2 and j3 are not the names of two identifiers. It is j·2 and j·3 where j is the imaginary constant. So (j2 - j3) = -j1.

    Personally I prefer putting the imaginary constant after the coefficient, but that's a matter of style.
     
    tjohnson likes this.
  16. WBahn

    Moderator

    Mar 31, 2012
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    Still, you should be able to explain why you did what you did based on your present understanding of the material. Otherwise you are just mimicking a monkey that is mimicking the instructor.
     
  17. Papabravo

    Expert

    Feb 24, 2006
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    Not quite
    A - B = (1 + j2) - (2 -j3) = (1 - 2) - (j2 - j3) = -1 - j1
     
  18. WBahn

    Moderator

    Mar 31, 2012
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    To show you what I mean, you should be able to apply normal algebra skills to factor out the j (remember, it's just a constant!)

    (1 + 2) + (j2 - j3) = (1 + 2) + j(2 - 3) = 3 + j(-1) = 3 - j1

    Use that same process for (1+2) - (j2 - j3)
     
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