Limits at Infinity Explore the End Behavior of a function
Dec 31, 2015
Limits at Infinity
Explore the End Behavior of a function
End Behavior
• The following is very important.
01
lim xx
01
lim xx
End Behavior
• The following is very important.• When the limit at infinity exists, it is known as the
horizontal asymptote.
Example 2
2tanlim 1
x
x 2tanlim 1
x
x
Example 3
• The following limits are one definition of e.
ex
x
x
11lim e
x
x
x
11lim
Polynomials
• We can generalize the end behavior of polynomials.
Polynomials
• We can generalize the end behavior of polynomials.• If the leading coefficient of the polynomial is positive:
n
xxlim
n
xxlim
,...5,3,1, n
,...6,4,2, n
Polynomials
• We can generalize the end behavior of polynomials.• If the leading coefficient of the polynomial is
negative:
n
xxlim
n
xxlim
,...5,3,1, n
,...6,4,2, n
Polynomials
• The end behavior of a polynomial matches the end behavior of its highest degree term.
Polynomials
• The end behavior of a polynomial matches the end behavior of its highest degree term.
• For example:
5lim xx
162lim 45 xxxx
Limits of Rational Functions
• We will have three different situations.
Limits of Rational Functions
• We will have three different situations.1. The degree of the numerator and the denominator is
the same.
Limits of Rational Functions
• We will have three different situations.1. The degree of the numerator and the denominator is
the same.2. The degree of the denominator is higher than the
degree of the numerator.
Limits of Rational Functions
• We will have three different situations.1. The degree of the numerator and the denominator is
the same.2. The degree of the denominator is higher than the
degree of the numerator.3. The degree of the numerator is higher than the
degree of the denominator.
Same Degree
• Find:86
53lim
x
xx
Same Degree
• Find:
• We will divide the numerator and denominator by the highest power of x in the denominator.
86
53lim
x
xx
x
xx 8
6
53
lim
Same Degree
• Find:
• We will divide the numerator and denominator by the highest power of x in the denominator.
86
53lim
x
xx
2
1
6
3lim
86
53
lim
xx
x
x
Same Degree
• When the numerator and the denominator are the same degree, your answer is a number, and it is the quotient of the leading coefficients.
Denominator is higher power
• We start the same way; divide the numerator and denominator by the highest power of x in the denominator.
• Find:
52
4lim
3
2
x
xxx
Denominator is higher power
• We start the same way; divide the numerator and denominator by the highest power of x in the denominator.
• Find:
33
3
33
2
3
2
52
4
52
4lim
xxx
xx
xx
x
xxx
Denominator is higher power
• We start the same way; divide the numerator and denominator by the highest power of x in the denominator.
• Find:
02
05
2
14
52
4
52
4lim
3
2
33
3
33
2
3
2
x
xx
xxx
xx
xx
x
xxx
Denominator is higher power
• Conclusion: When the denominator has the highest power of x, the answer is zero.
• For fractions, if the denominator accelerates faster than the numerator, the limit is zero.
Numerator is higher power
• We start the same way; divide the numerator and denominator by the highest power of x in the denominator.
• Find:
x
xxx 31
125lim
23
Numerator is higher power
• We start the same way; divide the numerator and denominator by the highest power of x in the denominator.
• Find:
xx
x
xxx
xx
x
xxx 31
125
31
125lim
23
23
Numerator is higher power
• We start the same way; divide the numerator and denominator by the highest power of x in the denominator.
• Find:
3
2531
125
31
125lim
2
23
23
xx
xx
x
xxx
xx
x
xxx
Numerator is higher power
• Conclusion: When the numerator is the higher power of x, the answer is .
• In the past example, the function reacts like a negative second degree equation, so the answer is
.
3
5
3
25lim
22 xxxx
Limits involving radicals
• Find:3
86
53lim
x
xx
Limits involving radicals
• Find:
3
86
53lim
x
xx
3
86
53lim
x
xx
Limits involving radicals
• Find:
33
2
1
86
53lim
x
xx
3
86
53lim
x
xx
Limits involving radicals
• Find:
63
2lim
2
x
xx
Limits involving radicals
• Find:
63
2lim
2
x
xx
||2 xx
||6
||3
2
lim22
2
xxx
xxx
x
Limits involving radicals
• Find:
• If x is approaching positive infinity, the absolute value of x is just x.
63
2lim
2
x
xx
||2 xx
xxxx
xxx
xxx
x 63
21
||6
||3
2
lim222
2
Limits involving radicals
• Find:
63
2lim
2
x
xx
||2 xx
3
16
3
21
||6
||3
2
lim222
2
x
x
xxx
xxx
x
Limits involving radicals
• Find:63
2lim
2
x
xx
||2 xx
Limits involving radicals
• Find:63
2lim
2
x
xx
||6
||3
2
lim22
2
xxx
xxx
x
||2 xx
Limits involving radicals
• Find:
• If x is approaching negative infinity, the absolute value of x is the opposite of x.
63
2lim
2
x
xx
3
163
21
||6
||3
2
lim222
2
xxx
x
xxx
xxx
x
||2 xx
Limits involving radicals
• Find: )5(lim 36 xxx
Limits involving radicals
• Find: )5(lim 36 xxx
3636
3636
5
5lim
)5(
)5()5(lim
xxxx
xxxx
xx
Limits involving radicals
• Find: )5(lim 36 xxx
3636
3636
5
5lim
)5(
)5()5(lim
xxxx
xxxx
xx
0101
0lim
3
3
66
6
3
5
5
xx
xxx
x
x
Limits involving radicals
• Find: )5(lim 336 xxxx
Limits involving radicals
• Find: )5(lim 336 xxxx
336
3
336
336336
5
5lim
)5(
)5()5(lim
xxx
x
xxx
xxxxxx
xx
Limits involving radicals
• Find: )5(lim 336 xxxx
336
3
336
336336
5
5lim
)5(
)5()5(lim
xxx
x
xxx
xxxxxx
xx
2
5
101
5lim
3
3
6
3
6
6
3
3
5
5
xx
xx
xx
xx
x
Limits of exponential and logarithmic functions
xx
lnlim x
xlnlim
0
Limits of exponential and logarithmic functions
• Let’s look at ex.
x
xelim 0lim
x
xe
Limits of exponential and logarithmic functions
• Let’s look at e-x
0lim
x
xe
x
xelim
Homework
• Section 1.3• Pages 96-97• 1-31odd