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Mathematical Expression Editor
Find limits using the Squeeze Theorem.
Squeeze Theorem
In this section we find limits using the Squeeze Theorem.
The Squeeze Theorem Suppose that the compound inequality holds for all values of
in some open interval about , except possibly for itself. If then we can conclude that as well.
Suppose for all except . Find
Since and we can use the Squeeze Theorem to conclude that as well.
Suppose that for all except . Find First, we find the limits of the bounds: Since
these answers are the same, the Squeeze Theorem allows us to conclude that
Find Since is undefined, plugging in does not give a definitive answer. Using the
fact that for all values of , we can create a compound inequality for the
function and find the limit using the Squeeze Theorem. To begin, note
that for all values of except . Multiplying this compound inequality by the
non-negative quantity we have for all values of except . Next, note that and
Finally, by the Squeeze Theorem, we can conclude that as well. The graph
below also shows that the limit is zero. Zoom in on the origin to get the full
effect.
Find using the Squeeze Theorem. First, we need to find bounds. Since for all ,
for all except . Next, we need to find the limits of those bounds: Since
these answers are the same, the Squeeze Theorem allows us to conclude that
The Squeeze Theorem can also be used if .
Find using the Squeeze Theorem. First, we need to find bounds. Since
for all , for all . Next, we need to find the limits of those bounds: Since
these answers are the same, the Squeeze Theorem allows us to conclude that
We conclude this section by using the Squeeze Theorem to find a special limit,
.
Consider the figure above. It consists of a small triangle, a sector of a circle of radius
and a large triangle. The area of the small triangle is The area of the sector is The area of the large
triangle is
We can use the areas of these figures to create a compound inequality like the one
found in the Squeeze theorem. Since the area of the small triangle is less than the
area of the sector which is less than the area of the large triangle, we have:
Multiply through by 2:
Divide through by . Note that if is a small positive angle, then so the direction of
the inequality symbols remains unchanged:
Next we take reciprocals (this will change the direction of the inequalitiy
symbols):
which is equivalent to
We now compute the limits of the upper and lower bounds:
Since the above limits are equal, the Squeeze Theorem applies and
To compute the left-hand limit, we note that for any angle . Therefore, which
implies that the left-hand limit and the right-hand limit are equal: