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    Let f be a non-constant entire function such that |f(z)| = 1 for |z| = 1.Let U denote the open unit disk around 0.Which of the following is FALSE ?
    Question

    Let f be a non-constant entire function such that |f(z)| = 1 for |z| = 1.

    Let U denote the open unit disk around 0.

    Which of the following is FALSE ?

    A.

    f(z) = C .

    B.

    f has at least one zero in U .

    C.

    f has at most finitely many distinct zeros in C .

    D.

    f can have a zero outside U.

    Correct option is D

    f(z) is a non-constant entire functionsuch that

    |f(z)| = 1 for |z| = 1.U = {z ∈ C | |z| < 1}

    According to the given condition f(z) will look like:f(z) = znz^n​ ; ∀z ∈ C .

    Stepwise Analysis:

    • Option (A) : As f(c) = c True.

    • Option (B) : f(z) = 0 ==> z = 0 , so f has at least one zero in U True.

    • Options (C) and (D) : clearly f can have at most finitely many distinctzeros in C,

    but f(z) cannot have a zero outside USo, Statement (D) is false

    ==> Option (D) is correct.

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