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GATE 2021 MA – Question 58

Complex Analysis · Complex Integration and Residues · 2 marks · Numerical answer

Count the zeros with multiplicity of P(z)=3z⁵+2iz²+7iz+1 in 1<|z|<7.

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Correct answer: 4 to 4

Explanation

On |z|=1, |7iz|=7 exceeds 3+2+1=6, so one zero lies in the unit disk. On |z|=7, |3z⁵|=50421 exceeds 2×49+7×7+1=148, giving five zeros in that disk. The strict inequalities exclude boundary zeros. Annulus count=5−1=**4**.

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