Paper 1, Section I, A

Vectors and Matrices | Part IA, 2016

Let z∈Cz \in \mathbb{C} be a solution of

z2+bz+1=0z^{2}+b z+1=0

where b∈Rb \in \mathbb{R} and ∣b∣⩽2|b| \leqslant 2. For which values of bb do the following hold?

(i) ∣ez∣<1\left|e^{z}\right|<1.

(ii) ∣eiz∣=1\left|e^{i z}\right|=1.

(iii) Im⁡(cosh⁡z)=0\operatorname{Im}(\cosh z)=0.

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