[tex]i^2 = -1 \quad $(identitate)$[/tex]
[tex](a-b)^2 = a^2-2\cdot a\cdot b + b^2[/tex]
[tex]z=1- i $ $ \Big|^2 \Rightarrow z^2 = (1-i)^2 \Rightarrow z^2 = 1^2-2\cdot i + i^2 \Rightarrow z^2 = 1 - 2i-1 \Rightarrow \\ \\ \Rightarrow \boxed{ z^2 = -2i}[/tex]
