Solve 5 < x² + 1 < 10

We can take 1 away from all elements to obtain 4 < x² < 9. Now, it's important to notice that when we square a negative, it gives us a positive, so when we take a square root to get 2 < x < 3 we could also get -2 > x > -3 because there is no way to know if we started with positives or negatives. The final answer is therefore "-2 > x > -3 or 2 < x < 3".