What interval consists of all u such that neither 2u nor 2u is in the interval (-1,1)?
+9519 Neither 2u nor 2u doesn't make much sense to me. Please check if that is a typo.
Anyways, if u is a number such that 2u is not in the interval (-1, 1), that means \(2u \leq -1\text{ or }2u \geq 1\). Solving each inequality gives \(u \leq -\dfrac12 \text{ or }u \geq \dfrac12\). Then the answer is \(\left(-\infty, -\dfrac12\right] \cup \left[\dfrac12, \infty\right)\)
