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Complex number proof

  1. May 11, 2007 #1
    w=cos(theta) + isin(theta) where 0<theta<pi
    if the complex number w^2 + (5/w) -2 = 0 is purely imaginary, show that 2cos^2 x + 5 cos (theta) -3=0.
    Hence, find w.

    any input would be appreciated, thx.
    Last edited: May 11, 2007
  2. jcsd
  3. May 11, 2007 #2


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    I'm a bit confused... if w^2 + (5/w) -2 = 0 is purely imaginary... why do you need to say it's purely imaginary? Don't we already know it's zero? Or is w pure imaginary (in which case we just know cos(theta)=0)?
  4. May 11, 2007 #3
    ahh good call. the complex number w^2 + (5/w) -2 is purely imaginary, doesnt necessarily equate to zero.
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