1. 2.2 Limits Involving Infinity
AP Calculus AB
2.2 Limits Involving Infinity

2. As the denominator gets larger, the value of the fraction gets smaller.
There is a horizontal asymptote if: or

3. Definition: Horizontal Asymptote
The line y = b is a a horizontal asymptote of the graph of a function y = f(x) if either:
For example:
y = -3 is the
horizontal asymptote.

4. Example 1 This number becomes insignificant as .
There is a horizontal asymptote at 1.

5. Use graphs and tables to find:
Example 2
Use graphs and tables to find:
Identify all horizontal asymptotes.
= 0
= -∞
y = 0
(the x-axis)

6. Use graphs and tables to find:
Example 3
Use graphs and tables to find:
Identify all horizontal asymptotes.
= 0
= 0
y = 0
First, graph on your calculator.
Next, use the table feature on your calculator to look at extremely large and small values for x.

7. Theorem 5: Properties of Limits
Limits at infinity have properties similar to those of finite limits.

8. Example 4
Find:
p Day 1

9. Infinite Limits:
As the denominator approaches zero, the value of the fraction gets very large.
vertical asymptote at x=0.
If the denominator is positive then the fraction is positive.
If the denominator is negative then the fraction is negative.

10. Finding Vertical Asymptotes
The denominator of any function cannot equal zero.
So, set the denominator equal to zero and solve.
The result is/are a vertical asymptote.

11. Find the vertical asymptotes of the graph of f(x).
Example 5
Find the vertical asymptotes of the graph of f(x).
Describe the behavior of f(x) to the left and right of each vertical asymptote.
Set x + 1 = 0.
The vertical asymptote is the line x = -1.

12. Example 5 (cont.)
To describe the behavior of f(x), substitute values to the left and right of the vertical asymptote.
So, let x = −0.5, then f(x) is a positive number, so
Next, let x = −1.5, then f(x) is a negative number, so

13. Example 6: Right-end behavior models give us:
dominant terms in numerator and denominator

14. End Behavior Models:
End behavior models model the behavior of a function as x approaches infinity or negative infinity.
The function g is:
a right end behavior model for f if and only if
a left end behavior model for f if and only if

15. Example 7: (The x term dominates.) As , approaches zero.
becomes a right-end behavior model.
Test of
model
Our model
is correct.
As , increases faster than x decreases,
therefore is dominant.
becomes a left-end behavior model.
Test of
model
Our model
is correct.

16. p Example 7 (cont.): becomes a right-end behavior model.
becomes a left-end behavior model.
On your calculator, graph:
Use: p