How do you find the limit lim_(x->0^-)|x|/x ?

1 Answer
Aug 2, 2014

When dealing with one-sided limits that involve the absolute value of something, the key is to remember that the absolute value function is really a piece-wise function in disguise. It can be broken down into this:

|x| =

x, when x>= 0
-x, when x< 0

You can see that no matter what value of x is chosen, it will always return a non-negative number, which is the main use of the absolute value function. This means that to evaluate this one-sided limit, we must figure out which version of this function is appropriate for our question.

Because our limit is approaching 0 from the negative side, we must use the version of |x| that is <0, which is -x. Rewriting our original problem, we have:

lim_(x->0^-)(-x)/x

Now that the absolute value is gone, we can divide the x term and now have:

lim_(x->0^-)-1

One of the properties of limits is that the limit of a constant is always that constant. If you imagine a constant on a graph, it would be a horizontal line stretching infinitely in both directions, since it stays at the same y-value regardless of what the x-value does. Since limits deal with finding what value a function "approaches" as it reaches a certain point, the limit of a horizontal line will always be a point along that line, no matter what x-value is chosen. Because of this, we now know:

lim_(x->0^-)-1 = -1, Giving us our final answer.