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hedipaldi
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Homework Statement
Let f(z) be holomorphic in the open unit disc taking real values only on the real axis.show that f has at most one zero in the open disc.
Homework Equations
Rouche's theorem,the argument principle.
The Attempt at a Solution
obviously,f does not have non-real zero's .I need help in counting the zero's by using the argument principle.
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