Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

manjuthottam

COMPLEX VARIABLES: Can someone explain how to find the Arg z and what does it mean?

  • one year ago
  • one year ago

  • This Question is Closed
  1. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    If I give you a complex number in \[a+bi\]form, do you know how to convert it to its "polar" form\[re^{i\theta}\]?

    • one year ago
  2. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    Because when written in its polar form:\[\arg(re^{i\theta})=\theta\]

    • one year ago
  3. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    where does a and b go?

    • one year ago
  4. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    I don't know how to convert it to its polar form, could you help me understand that formula?

    • one year ago
  5. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    |dw:1359087681895:dw|

    • one year ago
  6. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    r is the length of the complex number, given by using pythagorean theorem:\[r=\sqrt{a^2+b^2}\]

    • one year ago
  7. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    the angle is the argument. You use inverse tangent to get it.\[\theta=\tan ^{-1}(\frac{a}{b})\]

    • one year ago
  8. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    oh so r = modulus of the point (a,b)?

    • one year ago
  9. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    that is correct

    • one year ago
  10. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    so when asked arg z, it is the theta that they are asking for?

    • one year ago
  11. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    yes, they want the angle. Be careful when using that formula though. You need to make sure the answer you get reflects the right quadrant. Ex. arg(1+i) vs. arg(-1-i)

    • one year ago
  12. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    so when asked the arg of 1st quadrant, theta is by the formula you gave me; when asked the arg of quadrant 3, theta is tan inverse of (b/a) ?

    • one year ago
  13. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    ack! thanks for pointing out my mistake, it should be b/a in the formula i posted.

    • one year ago
  14. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    oh ok :)

    • one year ago
  15. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    the problem arises because inverse tangent always gives an angle between -pi/2 and pi/2, but you want an angle between 0 and 2pi. So if you were asked for the argument of -1-i, the formula would give pi/4 as an answer, but you know you want something in the 3rd quadrant, so you add pi to get the correct answer of 5\pi/4

    • one year ago
  16. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    oh ok that makes sense! Thanks!! may i ask another question related? How do i put it into the form of Re^(i theta)? actually what is that formula mean? is it just the form of the vector?

    • one year ago
  17. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    i understand how to get r and theta now, but i was wondering if it is a vector and why is there the 'e'?

    • one year ago
  18. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    Once you know the modulus and argument of a complex number, you know what r and theta are. Euler's formula says:\[e^{i\theta}=\cos\theta+i\sin\theta\]

    • one year ago
  19. joemath314159
    Best Response
    You've already chosen the best response.
    Medals 1

    Note that the modulus of e^(itheta)=1 since:\[|\cos\theta+i\sin\theta|=\cos ^2\theta+\sin^2\theta=1\]So the polar form of a complex number\[re^{i\theta}\]it really just saying, "i want a complex number whose length is r, in the direction of theta"

    • one year ago
  20. manjuthottam
    Best Response
    You've already chosen the best response.
    Medals 1

    oh i get it now!! I really appreciate you helping me!! Thank you so much!!

    • one year ago
    • Attachments:

See more questions >>>

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.