The original exercise is:
Which of the following is the solution set to \(\displaystyle \Big\lvert\, x\, -\, 5\, \Big\rvert \, < \, -1\)
?
F. the interval (4, 6)
G. the interval (-infinity, 4)
H. the interval (6, +infinity)
J. the intervals (-infinity, 4) and (6, +infinity)
K. the empty set
I tried to add 5 to both sides to get... x<4.
This would have resulted in the following new inequality:
. . . . .\(\displaystyle \Big\lvert\, x\, -\, 5\, \Big\rvert \, +\, 5\, <\, 4\)
How did you get from this to "x < 4"?
But that isn't correct because x = 3 doesn't work; it's untrue that 2<-1.
Does this not work because it's an inequality?
What is the "this" that "does...not work"?
To find the solution, it seems like you just have to use trial and error. Is that the only method of finding the solution?
No; whatever method they explained in the textbook should work. For further explanation of how to solve absolute-value inequalities, try
here. (If you're not familiar with how to solve absolute-value equations, you might want to start with lessons on that first.)
Please study at least two lessons from the list. Once you've learned the basic terms and techniques, please return to this exercise. You'll then understand why the first step has to be the removal of the absolute-value bars. Only then does adding things to either side (well, all three sides, at that point) do any good.