Results 1 to 5 of 5

Math Help - Argument of a complex number

  1. #1
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1

    Argument of a complex number

    Hi, sorry another problem with the argument of a complex number :S.

    1. Calculate arg z, giving your answer in radians to 2dp, where z = -1 + 2i.

    Got the answer -1.07, which is right as -\pi\leq-1.07\leq\pi, yet the answers have the answer as \pi + -1.07.

    Is this something I am missing, or just an odd answer?

    Thanks in advance
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Flow Master
    mr fantastic's Avatar
    Joined
    Dec 2007
    From
    Zeitgeist
    Posts
    16,948
    Thanks
    5
    Quote Originally Posted by craig View Post
    Hi, sorry another problem with the argument of a complex number :S.

    1. Calculate arg z, giving your answer in radians to 2dp, where z = -1 + 2i.

    Got the answer -1.07, which is right as -\pi\leq-1.07\leq\pi, yet the answers have the answer as \pi + -1.07.

    Is this something I am missing, or just an odd answer?

    Thanks in advance
    -1.07 is in the 4th quadrant. -1 + 2i is in the 2nd quadrant.

    You should always draw an argand diagram so you can see what quadrant z is in ....
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Quote Originally Posted by mr fantastic View Post
    -1.07 is in the 4th quadrant. -1 + 2i is in the 2nd quadrant.

    You should always draw an argand diagram so you can see what quadrant z is in ....
    Thank you
    Follow Math Help Forum on Facebook and Google+

  4. #4
    MHF Contributor

    Joined
    Aug 2006
    Posts
    18,924
    Thanks
    1762
    Awards
    1
    Craig, here is a simple scheme for doing the argument.
    \arg (z) = \arg (x + yi) = \left\{ {\begin{array}{ll}<br />
   {\arctan (y/x)} & {x > 0}  \\<br />
   {\arctan (y/x) + \pi } & {x < 0\,\& \,y > 0}  \\<br />
   {\arctan (y/x) - \pi } & {x < 0\,\& \,y < 0}  \\ \end{array} } \right.
    Follow Math Help Forum on Facebook and Google+

  5. #5
    Super Member craig's Avatar
    Joined
    Apr 2008
    Posts
    748
    Thanks
    1
    Awards
    1
    Quote Originally Posted by Plato View Post
    Craig, here is a simple scheme for doing the argument.
    \arg (z) = \arg (x + yi) = \left\{ {\begin{array}{ll}<br />
   {\arctan (y/x)} & {x > 0}  \\<br />
   {\arctan (y/x) + \pi } & {x < 0\,\& \,y > 0}  \\<br />
   {\arctan (y/x) - \pi } & {x < 0\,\& \,y < 0}  \\ \end{array} } \right.
    Thanks again Hopefully with this and drawing the diagram I should be ok
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Argument of a complex number
    Posted in the Differential Geometry Forum
    Replies: 2
    Last Post: August 22nd 2009, 02:22 PM
  2. Argument of complex number
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: April 3rd 2009, 08:06 PM
  3. Argument of a complex number
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: January 15th 2009, 12:39 PM
  4. [SOLVED] Argument of complex number
    Posted in the Calculus Forum
    Replies: 8
    Last Post: June 18th 2008, 03:29 PM
  5. argument of a complex number
    Posted in the Calculus Forum
    Replies: 1
    Last Post: April 2nd 2008, 01:08 PM

Search Tags


/mathhelpforum @mathhelpforum