Paper 1, Section I, A

Vectors and Matrices
Part IA, 2016

Let zCz \in \mathbb{C} be a solution of

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

where bRb \in \mathbb{R} and b2|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(coshz)=0\operatorname{Im}(\cosh z)=0.