Find the set of all $z$ such that neither $2+z$ nor $2-z$ is in the interval $(-1,1]$. Express your answer as an interval or as a union of i

By the way, it's supposed to be unit of intervals, not unit of i!

If 2+z is not in the interval (−1,1], then 2+z≤−1 or 2+z≥1. This gives us the two cases z≤−3 and z≥1. Similarly, if 2−z is not in the interval (−1,1], then 2−z≤−1 or 2−z≥1. This gives us the two cases z≥3 and z≤−1. Therefore, we are looking for all z such that z≤−3 or z≥3. This gives us the set (−∞,-3]∪[3,∞)​.