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Subsection 1.4.2 Exercises

Exercises — Stage 1

1

Suppose \(\displaystyle\lim_{x \rightarrow a} f(x)=0\) and \(\displaystyle\lim_{x \rightarrow a} g(x)=0\text{.}\) Which of the following limits can you compute, given this information?

  1. \(\displaystyle\lim_{x \rightarrow a} \frac{f(x)}{2}\)
  2. \(\displaystyle\lim_{x \rightarrow a} \frac{2}{f(x)}\)
  3. \(\displaystyle\lim_{x \rightarrow a} \frac{f(x)}{g(x)}\)
  4. \(\displaystyle\lim_{x \rightarrow a} f(x)g(x)\)
2

Give two functions \(f(x)\) and \(g(x)\) that satisfy \(\displaystyle\lim_{x \rightarrow 3}f(x)=\displaystyle\lim_{x \rightarrow 3}g(x)=0\) and \(\displaystyle\lim_{x \rightarrow 3} \dfrac{f(x)}{g(x)}=10\text{.}\)

3

Give two functions \(f(x)\) and \(g(x)\) that satisfy \(\displaystyle\lim_{x \rightarrow 3}f(x)=\displaystyle\lim_{x \rightarrow 3}g(x)=0\) and \(\displaystyle\lim_{x \rightarrow 3} \dfrac{f(x)}{g(x)}=0\text{.}\)

4

Give two functions \(f(x)\) and \(g(x)\) that satisfy \(\displaystyle\lim_{x \rightarrow 3}f(x)=\displaystyle\lim_{x \rightarrow 3}g(x)=0\) and \(\displaystyle\lim_{x \rightarrow 3} \dfrac{f(x)}{g(x)}=\infty\text{.}\)

5

Suppose \(\displaystyle\lim_{x \rightarrow a}f(x)=\displaystyle\lim_{x \rightarrow a}g(x)=0\text{.}\) What are the possible values of \(\displaystyle\lim_{x \rightarrow a}\dfrac{f(x)}{g(x)}\text{?}\)

Exercises — Stage 2

For Questions 1.4.2.6 through 1.4.2.41, evaluate the given limits.

6

\(\displaystyle\lim_{t \rightarrow 10} \dfrac{2(t-10)^2}{t}\)

7

\(\displaystyle\lim_{y \rightarrow 0} \dfrac{(y+1)(y+2)(y+3)}{\cos y}\)

8

\(\displaystyle\lim_{x \rightarrow 3} \left(\dfrac{4x-2}{x+2}\right)^4\)

9 (✳)

\(\ds \lim_{t\to -3} \left(\frac{1-t}{\cos(t)}\right)\)

10 (✳)

\(\ds \lim_{h \to 0} \frac{(2+h)^2-4}{2h}\)

11 (✳)

\(\ds \lim_{t\to -2} \left(\frac{t-5}{t+4}\right)\)

12 (✳)

\(\ds \lim_{x\to 1} \sqrt{5x^3 + 4}\)

13 (✳)

\(\displaystyle\lim_{t\rightarrow -1} \left(\frac{t-2}{t+3}\right)\)

14 (✳)

\(\lim\limits_{x\rightarrow 1}\dfrac{\log(1+x)-x}{x^2}\)

15 (✳)

\(\displaystyle\lim_{x\rightarrow 2} \left(\frac{x-2}{x^2-4}\right)\)

16 (✳)

\(\ds\lim\limits_{x\rightarrow 4}\dfrac{x^2-4x}{x^2-16}\)

17 (✳)

\(\lim\limits_{x\rightarrow 2}\dfrac{x^2+x-6}{x-2}\)

18 (✳)

\(\ds \lim_{x \to -3} \frac{x^2-9}{x+3}\)

19

\(\displaystyle\lim_{t \rightarrow 2} \frac{1}{2}t^4-3t^3+t\)

20 (✳)

\(\ds \lim_{x\to -1} \frac{\sqrt{x^2+8}-3}{x+1}\text{.}\)

21 (✳)

\(\ds \lim_{x\to 2} \frac{\sqrt{x+7}-\sqrt{11-x}}{2x-4}\text{.}\)

22 (✳)

\(\displaystyle \lim_{x\rightarrow 1} \frac{\sqrt{x+2}-\sqrt{4-x}}{x-1}\)

23 (✳)

\(\ds \lim_{x\to 3} \frac{\sqrt{x-2}-\sqrt{4-x}}{x-3}\text{.}\)

24 (✳)

\(\ds \lim_{t\to 1} \frac{3t-3}{2 - \sqrt{5-t}}\text{.}\)

25

\(\displaystyle\lim_{x \rightarrow 0}-x^2\cos\left(\frac{3}{x}\right)\)

26

\(\displaystyle\lim_{x \rightarrow 0}\dfrac{x^4\sin\left(\frac{1}{x}\right)+5x^2\cos\left(\frac{1}{x}\right)+2}{(x-2)^2}\)

27 (✳)

\(\lim\limits_{x\rightarrow 0}x\sin^2\left(\dfrac{1}{x}\right)\)

28

\(\displaystyle\lim_{w \rightarrow 5} \dfrac{2w^2-50}{(w-5)(w-1)}\)

29

\(\displaystyle\lim_{r \rightarrow -5} \dfrac{r}{r^2+10r+25}\)

30

\(\displaystyle\lim_{x \rightarrow -1}\sqrt{\dfrac{x^3+x^2+x+1}{3x+3}}\)

31

\(\displaystyle\lim_{x \rightarrow 0} \dfrac{x^2+2x+1}{3x^5-5x^3}\)

32

\(\displaystyle\lim_{t \rightarrow 7} \dfrac{t^2x^2+2tx+1}{t^2-14t+49}\text{,}\) where \(x\) is a positive constant

33

\(\displaystyle\lim_{d \rightarrow 0} x^5-32x+15\text{,}\) where \(x\) is a constant

34

\(\displaystyle\lim_{x \rightarrow 1} (x-1)^2\sin\left[\left(\dfrac{x^2-3x+2}{x^2-2x+1}\right)^2+15\right]\)

35 (✳)

Evaluate \(\ds \lim_{x\rightarrow 0} x^{1/101} \sin\big(x^{-100}\big)\) or explain why this limit does not exist.

36 (✳)

\(\lim\limits_{x\rightarrow2}\dfrac{x^2-4}{x^2-2x}\)

37

\(\displaystyle\lim_{x \rightarrow 5} \dfrac{(x-5)^2}{x+5}\)

38

Evaluate \(\ds\lim_{t \to \frac{1}{2}}\dfrac{\frac{1}{3t^2}+\frac{1}{t^2-1}}{2t-1}\) .

39

Evaluate \(\ds\lim_{x \to 0}\left( 3+\dfrac{|x|}{x}\right) \text{.}\)

40

Evaluate \(\ds\lim_{d \to -4}\dfrac{|3d+12|}{d+4}\)

41

Evaluate \(\ds\lim_{x \to 0}\dfrac{5x-9}{|x|+2}\text{.}\)

42

Suppose \(\displaystyle\lim_{x \rightarrow -1} f(x)=-1\text{.}\) Evaluate \(\displaystyle\lim_{x \rightarrow -1} \dfrac{xf(x)+3}{2f(x)+1}\text{.}\)

43 (✳)

Find the value of the constant \(a\) for which \(\lim\limits_{x\rightarrow -2}\dfrac{x^2+ax+3}{x^2+x-2}\) exists.

44

Suppose \(f(x)=2x\) and \(g(x)=\frac{1}{x}\text{.}\) Evaluate the following limits.

  1. \(\displaystyle\lim_{x \rightarrow 0} f(x)\)
  2. \(\displaystyle\lim_{x \rightarrow 0} g(x)\)
  3. \(\displaystyle\lim_{x \rightarrow 0} f(x)g(x)\)
  4. \(\displaystyle\lim_{x \rightarrow 0} \dfrac{f(x)}{g(x)}\)
  5. \(\displaystyle\lim_{x \rightarrow 2} [f(x)+g(x)]\)
  6. \(\displaystyle\lim_{x \rightarrow 0} \dfrac{f(x)+1}{g(x+1)}\)

Exercises — Stage 3

45

The curve \(y=f(x)\) is shown in the graph below. Sketch the graph of \(y=\dfrac{1}{f(x)}\text{.}\)

46

The graphs of functions \(f(x)\) and \(g(x)\) are shown in the graphs below. Use these to sketch the graph of \(\dfrac{f(x)}{g(x)}\text{.}\)

47

Suppose the position of a white ball, at time \(t\text{,}\) is given by \(s(t)\text{,}\) and the position of a red ball is given by \(2s(t)\text{.}\) Using the definition from Section 1.2 of the velocity of a particle, and the limit laws from this section, answer the following question: if the white ball has velocity 5 at time \(t=1\text{,}\) what is the velocity of the red ball?

48

Let \(f(x) = \frac{1}{x}\) and \(g(x) = \frac{-1}{x}\text{.}\)

  1. Evaluate \(\displaystyle\lim_{x \rightarrow 0} f(x)\) and \(\displaystyle\lim_{x \rightarrow 0} g(x)\text{.}\)
  2. Evaluate \(\displaystyle\lim_{x \rightarrow 0} [f(x)+g(x)]\)
  3. Is it always true that \(\displaystyle\lim_{x \rightarrow a} [f(x)+g(x)]= \displaystyle\lim_{x \rightarrow a} f(x)+\displaystyle\lim_{x \rightarrow a} g(x)\text{?}\)
49

Suppose

\begin{align*} f(x) &=\begin{cases} x^2+3 & \text{ if } x\gt 0\\ 0 & \text{ if } x = 0\\ x^2-3 & \text{ if } x \lt 0 \end{cases} \end{align*}
  1. Evaluate \(\displaystyle\lim_{x \rightarrow 0^-} f(x)\text{.}\)
  2. Evaluate \(\displaystyle\lim_{x \rightarrow 0^+} f(x)\text{.}\)
  3. Evaluate \(\displaystyle\lim_{x \rightarrow 0} f(x)\text{.}\)
50

Suppose

\begin{align*} f(x) &=\begin{cases} {\displaystyle\frac{x^2+8x+16}{x^2+30x-4}} & \text{ if } x\gt -4\\ x^3+8x^2+16x & \text{ if } x \le -4 \end{cases} \end{align*}
  1. Evaluate \(\displaystyle\lim_{x \rightarrow -4^-} f(x)\text{.}\)
  2. Evaluate \(\displaystyle\lim_{x \rightarrow -4^+} f(x)\text{.}\)
  3. Evaluate \(\displaystyle\lim_{x \rightarrow -4} f(x)\text{.}\)