Hi there! |2x + 1| (greater than or equal to) 3. So the absolute value of an equation always results in a positive equation. If you haven't done negative integers yet, here..
|-4| = 4
|-3| = 3
|-2| = 2
-4 = -4
-3 = -3
-2 = -2
But when you put the absolute value marks next to them, the value turns positive. :D
So |2x + 1| is greater than or equal to 3. The number for x can be negative, since the equation is always turned positive. |2(-1) + 1| = 3 is 2(1) + 1 = 3. So yes, -1 would work. But then again, positive 1 will work too! The value just can't be zero, since that would be 2(0) + 1 = 3, which is 0 + 1 = 3, not true.
Values have to be [1, +infinity] and [-1, -infinity].
Hope that helps!