Section 2.3 : One-Sided Limits
2. Below is the graph of f(x). For each of the given points determine the value of f(a), limx→a−f(x), limx→a+f(x), and limx→af(x). If any of the quantities do not exist clearly explain why.
- a=−2
- a=1
- a=3
- a=5

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a a=−2 Show SolutionFrom the graph we can see that,
f(−2)=−1because the closed dot is at the value of y=−1.
We can also see that as we approach x=−2 from the left the graph is not approaching a single value, but instead oscillating wildly, and as we approach from the right the graph is approaching a value of -1. Therefore, we get,
limx→−2−f(x) does not exist&,limx→−2+f(x)=−1Recall that in order for limit to exist the function must be approaching a single value and so, in this case, because the graph to the left of x=−2 is not approaching a single value the left-hand limit will not exist. This does not mean that the right-hand limit will not exist. In this case the graph to the right of x=−2 is approaching a single value the right-hand limit will exist.
Now, because the two one-sided limits are different we know that,
limx→−2f(x)does not existb a=1 Show Solution
From the graph we can see that,
f(1)=4because the closed dot is at the value of y=4.
We can also see that as we approach x=1 from both sides the graph is approaching the same value, 3, and so we get,
limx→1−f(x)=3&limx→1+f(x)=3The two one-sided limits are the same so we know,
limx→1f(x)=3c a=3 Show Solution
From the graph we can see that,
f(3)=−2because the closed dot is at the value of y=−2.
We can also see that as we approach x=2 from the left the graph is approaching a value of 1 and as we approach from the right the graph is approaching a value of -3. Therefore, we get,
limx→3−f(x)=1&limx→3+f(x)=−3Now, because the two one-sided limits are different we know that,
limx→3f(x)does not existd a=5 Show Solution
From the graph we can see that,
f(5)=4because the closed dot is at the value of y=4.
We can also see that as we approach x=5 from both sides the graph is approaching the same value, 4, and so we get,
limx→5−f(x)=4&limx→5+f(x)=4The two one-sided limits are the same so we know,
limx→5f(x)=4