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Sistine
Jan11-10, 08:55 AM
1. The problem statement, all variables and given/known data
Prove that if f is a meromorphic function f:\mathbb{C}\rightarrow\mathbb{C} with

|f(z)|^5\leq |z|^6\quad\textrm{for all}\quad z\in\mathbb{C}

Then f(z)=0 for all z\in\mathbb{C}

2. Relevant equations
Liouville's Theorem

A bounded entire function is constant.

3. The attempt at a solution
I tried applying Liouville's theorem to the quotient f(z)^5/z^6 which is bounded by 1 but was unsuccessful in proving that f is constant.

JSuarez
Jan11-10, 10:52 AM
Note that the hypothesis implies that f(z)^5/z^6 is a bounded function but because of the z^6 in the denominator, you must prove that it's also entire.

To prove this, note (again, by the hypothesis) that f(z) must have a zero at the origin, so either f(z) is identically zero, or f(z) = z^ng(z); but then

f(z)^5/z^6=z^{5n}g(z)^5/z^6

And this implies that n > 1 . After simplifying, what can you say about g(z)?