Limits and Continuity 59
Example 4
Find: limx→ 2 −
[x]−x
2 −x
, where [x] is the greatest integer value ofx.
Asx→ 2 −,[x]=1. The limit of the numerator is (1−2)=−1. Asx→ 2 −,(2−x)= 0
through positive values. Thus, limx→ 2 −
[x]−x
2 −x
=−∞.
TIP • Do easy questions first. The easy ones are worth the same number of points as the hard
ones.
Limits at Infinity (asx→±∞)
If f is a function defined at every number in some interval (a,∞), then limx→∞f(x)=L
means thatLis the limit off(x)asxincreases without bound.
If fis a function defined at every number in some interval (−∞,a), then limx→−∞f(x)=L
means thatLis the limit off(x)asxdecreases without bound.
Limit Theorem
Ifnis a positive integer, then
(a) xlim→∞
1
xn
= 0
(b) xlim→−∞
1
xn
= 0
Example 1
Evaluate the limit: limx→∞
6 x− 13
2 x+ 5
.
Divide every term in the numerator and denominator by the highest power ofx(in this
case, it isx), and obtain:
xlim→∞
6 x− 13
2 x+ 5
=xlim→∞
6 −
13
x
2 +
5
x
=
xlim→∞(6)−xlim→∞
13
x
xlim→∞(2)+xlim→∞
(
5
x
)=
xlim→∞(6)−13 limx→∞
(
1
x
)
xlim→∞(2)+5 limx→∞
(
1
x
)
=
6 −13(0)
2 +5(0)
= 3.
Verify your result with a calculator. (See Figure 5.2-3.)
[–10,30] by [–5,10]
Figure 5.2-3