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Homework Help: Easy Question for y'all

  1. Apr 27, 2012 #1
    Plot the set of points which satisy


    Im not sure about how to do this.

    Sorry im sure its very simple for you but can you just explain how to do one of them? I started maths later in life so im not solid in mathematics.

    Thanks a lot :-)
  2. jcsd
  3. Apr 27, 2012 #2

    What is "I", "z", "j" ...??

  4. Apr 27, 2012 #3
    Sorry we use 'j' instead of 'i' for imaginary numbers because i usually means current in electrical engineering. Im not doing electrical but i need to know the math apparently..

    im not sure about z, i though z means the complex number.. i dont understand the q

    The capital I is just supposed to represent the bar things on either side of the equation i forget what they are called..
  5. Apr 27, 2012 #4


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    Staff: Mentor

    Oh, well that's cleared that up! cMtyZ.gif

    So you are wanting to plot on the complex plane the set of points which satisfy
    Code (Text):
    (i) magnitude(z+1+i)=2

    I'm a bit rusty on z stuff myself. Let's start off by replacing z by x + iy

    magnitude(x+iy+1+i) = 2

    Collecting real and imaginary,
    ⇒magnitude({x+1} + i{1+y}) = 2

    That's a single complex number inside the ( ). How do you write its magnitude?
  6. Apr 27, 2012 #5

    Wow, now I see...lol! Those bars, you should know, are called "absolute value" or "module of a complex number"...! So you actually meant to solve [tex]|z+1+i|=2[/tex][tex]|2z+3|\leq 1[/tex]

    Let [itex]\displaystyle{z=a+bi\,,\,\,a,b\in\mathbb R}[/itex] and substitute in the equations above.
    Mod note: Removed a too-complete answer.
    Last edited by a moderator: Apr 27, 2012
  7. Apr 27, 2012 #6


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    Staff: Mentor

    DonAntonio, the philosophy of physics forums is to not provide a complete homework solution without encouraging some contribution from the OP. Despite its location in the general forum, this has every appearance of being a homework or assignment question.

    And the word is "modulus".
  8. Apr 29, 2012 #7
    Thank you so much DonAntonio. Though It would have been much better and less of a waste of your time if I could have seen the rest of your answer.

    Moderator. Do you enjoy treating people like children?? This isnt high school homework! This is an example of a question which I didn't quite understand due to not being shown any examples at the night classes I attend to try and get my engineering degree. There will possibly be a similar question on the test,. Thanks for the hindrance in what is already a great challenge and the condescending attitude, I dont think there is any point being on this forum if its going to be so fascist.
  9. Apr 29, 2012 #8


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    Staff Emeritus
    Science Advisor
    Homework Helper
    Gold Member

    The moderator (who does his/her work here as a volunteer) was merely enforcing the rules of this Forum.

    Physics Forum appears to be helpful to many of those who come here seeking help. We regret it if you feel you were not helped.
  10. Apr 29, 2012 #9


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    Staff: Mentor

    Was my intro to help you get started with this example not sufficiently encouraging? https://www.physicsforums.com/showpost.php?p=3886532&postcount=4
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