Results 1 to 7 of 7

Math Help - Complex Number, De Moivre and all those kinds of goodies!

  1. #1
    Junior Member JoeyCC's Avatar
    Joined
    Nov 2008
    From
    Brazil
    Posts
    40

    Complex Number, De Moivre and all those kinds of goodies!

    Well, this week I have a test on my worst mathematics topic so far. Complex Number. For me, someone who's not that bright, this is simply incomprehensible. I was wondering if someone could explain, in simple language and in digestable way, how to:


    • Work with complex numbers and learning to equate them
    • Cis form (cos thetha + isin theta) and all that rubbish
    • De Moivre's Theorem

    All the aid is strongly appreciated!

    Please make it simple for me!

    ~Kindest Regards
    Follow Math Help Forum on Facebook and Google+

  2. #2
    MHF Contributor Mathstud28's Avatar
    Joined
    Mar 2008
    From
    Pennsylvania
    Posts
    3,641
    [quote=JoeyCC;229388]Well, this week I have a test on my worst mathematics topic so far. Complex Number. For me, someone who's not that bright, this is simply incomprehensible. I was wondering if someone could explain, in simple language and in digestable way, how to:

    • Work with complex numbers and learning to equate them
    I am not too sure what you mean? Could you give an example?




    • Cis form (cos thetha + isin theta) and all that rubbish


    We define the function \text{cis}(x) to be

    \text{cis}(x)=e^{ix}

    And by Euler's formula we have that e^{ix}=\cos(x)+i\sin(x)

    So

    \text{cis}(x)=\cos(x)+i\sin(x)

    If you have any specific quetions just ask

    • De Moivre's Theorem
    This is simply saying

    \left(\cos(x)+i\sin(x)\right)^n=\cos(nx)+i\sin(nx)

    The simple reason is

    \begin{aligned}\left(\cos(x)+i\sin(x)\right)^n&=\l  eft(e^{ix}\right)^n\\<br />
&=e^{inx}\\<br />
&=\cos(nx)+i\sin(nx)\end{aligned}


    Do you have any specific problems or examples we could use to help explain any of these concepts?
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Junior Member JoeyCC's Avatar
    Joined
    Nov 2008
    From
    Brazil
    Posts
    40
    Firstly, I am having difficulties deducing stuff like:

    why \sqrt3 + i = 2(\sqrt(\dfrac{3}{2}) + \dfrac{1}{2}i)

    and then why 2(\sqrt 3/2 + \dfrac{1}{2}i) = 2 cis pi/6
    Follow Math Help Forum on Facebook and Google+

  4. #4
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by JoeyCC View Post
    Well, this week I have a test on my worst mathematics topic so far. Complex Number. For me, someone who's not that bright, this is simply incomprehensible. I was wondering if someone could explain, in simple language and in digestable way, how to:


    • Work with complex numbers and learning to equate them
    • Cis form (cos thetha + isin theta) and all that rubbish
    • De Moivre's Theorem
    All the aid is strongly appreciated!

    Please make it simple for me!

    ~Kindest Regards
    Sorry, but what you're asking is not reasonable. This material covers several hours worth of class room teaching time.

    Read your textbook and class notes. Ask your teacher for help. These Forums are not a substitute for classroom teaching.

    You should be asking for help as you need it rather than waiting until you have a test and then asking for help on the entire topic. Keep that in mind when you start your next topic.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Junior Member JoeyCC's Avatar
    Joined
    Nov 2008
    From
    Brazil
    Posts
    40
    Excuse me sir, but I then asked a specific question:

    Quote Originally Posted by JoeyCC View Post
    Firstly, I am having difficulties deducing stuff like:

    why \sqrt3 + i = 2(\sqrt(\dfrac{3}{2}) + \dfrac{1}{2}i)

    and then why 2(\sqrt 3/2 + \dfrac{1}{2}i) = 2 cis pi/6
    Follow Math Help Forum on Facebook and Google+

  6. #6
    Member Greengoblin's Avatar
    Joined
    Feb 2008
    From
    UK
    Posts
    182
    2\left(\sqrt{\left(\frac{3}{2}\right)}+\frac{1}{2}  i\right)=2\left(\frac{3}{2}\right)^{1/2}+2\frac{1}{2}i=\frac{2\sqrt3}{\sqrt{2}}+i=\sqrt{  6}+i\ne\sqrt{3}+i
    Follow Math Help Forum on Facebook and Google+

  7. #7
    MHF Contributor
    Joined
    Oct 2005
    From
    Earth
    Posts
    1,599
    Quote Originally Posted by JoeyCC View Post
    Excuse me sir, but I then asked a specific question:
    Excuse me, but please treat all users (especially staff members) with respect. Your original post for this thread was very vague and not the type of help we provide. Your second post in this thread is more like it.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Buying two different kinds of toys.
    Posted in the Algebra Forum
    Replies: 3
    Last Post: November 7th 2011, 09:25 PM
  2. Complex Algebra (De Moivre?)
    Posted in the Algebra Forum
    Replies: 2
    Last Post: January 18th 2011, 08:15 AM
  3. Complex number with De Moivre's formula
    Posted in the Calculus Forum
    Replies: 2
    Last Post: December 17th 2010, 05:37 AM
  4. Complex number - De Moivre
    Posted in the Calculus Forum
    Replies: 2
    Last Post: June 2nd 2010, 01:54 PM
  5. Math Goodies
    Posted in the Math Forum
    Replies: 0
    Last Post: March 25th 2007, 04:21 PM

Search Tags


/mathhelpforum @mathhelpforum