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Homework Help: Fundamental Theorem of Algebra Proof

  1. Sep 28, 2011 #1
    Hello, trying to figure out exactly what is going on in this question.

    1. The problem statement, all variables and given/known data

    (a) If P(z) is a nonconstant polynomial, show that |P(z)| > |P(0)| holds outside
    some disk R |z| ≤ R for some R > 0. Conclude that if the minimum value of |P(z)| for R
    z ≤ |R| occurs at z_o, then z=z_o gives the minimum value of |P(z)| with respect to the whole complex plane.

    2. Relevant equations

    3. The attempt at a solution

    P(z) = a0+a1*z1+a2*z^2+...+an*zn^n
    |P(z)| = |a0+a1*z1+a2*z^2+...+an*zn^n|
    |P(z)| = |Z**n||a0*z^-n+a1*z1^1-n+a2*z^2-n+...+an|

    I know that I have to show that P(z) grows faster than P(0) for it to hold outside the disk. But I am not sure what that even means for an inequality to hold outside of a disk. I really don't know what it is asking.
  2. jcsd
  3. Sep 28, 2011 #2


    User Avatar
    Science Advisor

    Well, where, exactly, is your difficulty? Do you know what a "disk" is? Do you know what is meant by "outside of a disk"? Do you know what it means for "an inequality to hold"?
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