What does "$z\in\Bbb{C}\setminus\{i,-2\}$" mean? [closed]
What does "$z\in\Bbb{C}\setminus\{i,-2\}$" (as highlighted in yellow below) mean?
If you have two sets, $A$ and $B$, then $A \backslash B$. The elements of this new set are all elements that belong to $A$ but don't belong to $B$: $$x \in A \backslash B \iff x\in A \wedge x \notin B$$
So the set $\mathbb C \backslash\{i, -2\}$ is the set of all complex numbers without $i$ and $-2$.