Math 137 Online Week 4 Outline and Practice Problems
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Math 137Online
Week 4 Outline and Practice Problems
This week, we’ll be covering more limits of functions.
Reading & Videos
● (Course notes available here)
● Section 2.2 - Uniqueness of Limits
● Section 2.2 - Sequential Characterization of Limits
● Section 2.3 - Arithmetic Rules for Limits of Functions
● Section 2.4 - One-sided limits
● Section 2.5 - Squeeze Theorem for Limits of Functions
● Section 2.6 - Fundamental Trig Limit
Practice Problems
1. Use the e 一 δ definition of limits to establish the following:
(a) lim 2x + 1 = 7
xo3
(b) lim 1 一 9x = 10
xo二1
(c) lim 3 = 3 xo5
(d) lim x2 一 4x + 4 = 0 xo2
(e) lim 1 = 1
2. Let f(x) > 0 for all x a and assume lim f(x) = L with L 士&. Use the definition of limits to xoa
show that L ≥ 0. Hint: build a contradiction by assuming L < 0.
3. For the following limits, lim f(x), find a sequence xn such that xn → a, xn a and then use this
sequence to show that the limits do not exist.
(a) lim 1
(b) lim ln lxl
xo0
4. Prove that lim does not exist by finding two sequences xn and yn that both converge to 3,
xn 3, yn 3 for all n ∈ N, and lim f(xn ) lim f(yn ). Explain why this proves the limit does
not exist.
5. Compute the following limits using any method. If they do not exist, prove it.
x2 一 16
xo4 x 一 4
x3 一 6x2 + 12x 一 8
xo2 x 一 2
^x 一 4
xo16 x 一 16
tan2 (x) + 1
xoπ/2 sec2 (x)
l3x 一 9l
xo3 3 一 x
(f)x(l)imo1 f (x) with f (x) = ,lx(1)一(一)11(l)
6. Consider the function
x < b
x > b
Determine all values of b ∈ R for which lim f (x) exists. Find the limit in each case. Prove that the
xob
limit does not exist for any other choice of b.
7. Compute the following limits (without using l’Hopital’s rule, if you are familiar with it):
sin2 (x)
xo0 x2
1 一 cos(x)
xo0 x2
sin[3(x2 一 4)]
xo2 x 一 2
sin(x2 )
xo0 ′ lx3 l
Practice Quiz
1. Consider the function f (x) = x . Which of the following are true?
(a) lim f (x) does not exist
xo0
(b) lim f (x) = 0
xo0
(c) lim f (x) = 1 xo0
f (x)
xo0 x
(e) lim xf (x) = 1
xo0
(f) None of the above.
2. Suppose that we fix e > 0. To prove that lim 3x + 2 = 14, which of the following are acceptable xo4
choices for 6?
e
(a) 6 =
e
(b) 6 =
e
(c) 6 =
(e) 6 = +
2023-02-13