1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Finding polar form of complex number

  1. Nov 19, 2015 #1
    1. The problem statement, all variables and given/known data
    I have the following complex numbers : -3,18 +4,19i
    I must put it in polar form.

    2. Relevant equations
    cos x = a/r
    sin x = b/r

    3. The attempt at a solution

    I was able to find with cos x = a/r that the x = 127,20

    But when I do it with sin x = b/r I obtain like 52 degrees. I know that I Must obtain 127,20 for BOTH. Why isnt it working ?
  2. jcsd
  3. Nov 19, 2015 #2


    User Avatar
    Science Advisor
    Gold Member

    The sin of both those angles are the same, so you must decide which is correct. That is the angle that has the correct a,b values. 52 degrees would be at (3.18, 4.19) and 127.2 degrees is at (-3.18, 4.19).
  4. Nov 19, 2015 #3
    Oh ok so its normal that I obtain two different values. Ok then, thank you!
  5. Nov 20, 2015 #4


    User Avatar
    Staff Emeritus
    Science Advisor

    Yes, There are always two values of [itex]\theta[/itex] in the interval 0 to [itex]2\pi[/itex] that have the same [itex]sin(\theta)[/itex]. But you still have to determine which is correct for the specific problem- the two different values, [itex]\theta[/itex] have different values for [itex]cos(\theta)[/itex].
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted

Similar Discussions: Finding polar form of complex number