Complex Numbers - Nomenclature

Maths and statistics discussion, revision, exam and homework help.

Announcements Posted on
Please change your TSR password 23-05-2013
Enter our travel-writing competition for the chance to win a Nikon 1 J3 camera 20-05-2013
IMPORTANT: You must wait until midnight (morning exams)/4.30AM (afternoon exams) to discuss Edexcel exams and until 1pm/6pm the following day for STEP and IB exams. Please read before posting, including for rules for practical and oral exams. 28-04-2013
Sign in to Reply
  1. ViralRiver's Avatar
    • Overlord in Training
    • Posts: 2,408
    Complex Numbers - Nomenclature
    Okay, I had a question where I was given a simple complex number in the form a+bi, and asked to put it in polar form. So I changed it to \sqrt{a^2+b^2}[cos(\theta )+isin(\theta )], \theta =\frac{b}{a}. However the answer was in the form of \sqrt{a^2+b^2}e^i{\theta }, \theta =\frac{b}{a}. I was under the impression that this was the "Euler form".

    Can someone just clear up which form is which so I am not confused from now on !
  2. Bobifier's Avatar
    • TSR Demigod
    • Location: England
    • Posts: 5,613
    Re: Complex Numbers - Nomenclature
    Polar form just means in terms of it's distance from the origin (its 'radius') and its angle from 1. Both of the forms you have given would qualify as some kind of polar form but writing it as an exponent of e is the most common way since it has the same amount of information and is easier to write.
  3. SZRoberson's Avatar
    • New Member
    • Location: San Diego, CA
    • Posts: 12
    Re: Complex Numbers - Nomenclature
    I would always write a complex number in the form  r\ cis(\theta), where r is the modulus of the complex number and  cis(\theta) is another way of saying  cos(\theta)+i\ sin(\theta) . That's polar form to me.

    I almost never use Euler's formula unless I'm proving its validity by the Maclaurin series.
  4. DFranklin's Avatar
    • TSR Royalty
    • Location: London
    • Posts: 18,052
    Re: Complex Numbers - Nomenclature
    At degree level I'd say re^{i\theta} is very much the canonical form for a polar representation.
  5. Jake22's Avatar
    • TSR Demigod
    • Posts: 5,176
    Re: Complex Numbers - Nomenclature
    I would agree that re^{i\theta} is much more standard than r(\cos \theta + i \sin \theta) or the quite ugly r \operatorname{cis}\theta.

    However, as usual, if you are answering a question from your course, then what your lecturer/teacher means by 'polar form' will be contained within the content of your course i.e. will have been mentioned in lessons/lectures/the book/lecture notes etc. So the first call would be to reexamine those. I am nearly sure, however, that if you have covered Euler's formula then your teacher/lecturer will either:

    a) decree re^{i\theta} as standard polar form or
    b) accept either way of writing it.
Sign in to Reply
Share this discussion:  
Article updates
Moderators

We have a brilliant team of more than 60 volunteers looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

Reputation gems:
The Reputation gems seen here indicate how well reputed the user is, red gem indicate negative reputation and green indicates a good rep.
Post rating score:
These scores show if a post has been positively or negatively rated by our members.