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Mathematics LibreTexts

8.5E: Exercises

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    Practice Makes Perfect

    Exercise SET A: divide square roots

    In the following exercises, simplify.

    1. a. \(\dfrac{\sqrt{128}}{\sqrt{72}}\quad\) b. \(\dfrac{\sqrt[3]{128}}{\sqrt[3]{54}}\)

    2. a. \(\dfrac{\sqrt{48}}{\sqrt{75}}\quad\) b. \(\dfrac{\sqrt[3]{81}}{\sqrt[3]{24}}\)

    3. a.\(\dfrac{\sqrt{200 m^{5}}}{\sqrt{98 m}}\quad\) b. \(\dfrac{\sqrt[3]{54 y^{2}}}{\sqrt[3]{2 y^{5}}}\)

    4. a. \(\dfrac{\sqrt{108 n^{7}}}{\sqrt{243 n^{3}}}\quad\) b. \(\dfrac{\sqrt[3]{54 y}}{\sqrt[3]{16 y^{4}}}\)

    5. a. \(\dfrac{\sqrt{75 r^{3}}}{\sqrt{108 r^{7}}}\quad\) b. \(\dfrac{\sqrt[3]{24 x^{7}}}{\sqrt[3]{81 x^{4}}}\)

    6. a. \(\dfrac{\sqrt{196 q}}{\sqrt{484 q^{5}}}\quad\) b. \(\dfrac{\sqrt[3]{16 m^{4}}}{\sqrt[3]{54 m}}\)

    7. a. \(\dfrac{\sqrt{108 p^{5} q^{2}}}{\sqrt{3 p^{3} q^{6}}}\quad\) b. \(\dfrac{\sqrt[3]{-16 a^{4} b^{-2}}}{\sqrt[3]{2 a^{-2} b}}\)

    8. a. \(\dfrac{\sqrt{98 r s^{10}}}{\sqrt{2 r^{3} s^{4}}}\quad\) b. \(\dfrac{\sqrt[3]{-375 y^{4} z^{2}}}{\sqrt[3]{3 y-2 z^{4}}}\)

    9. a. \(\dfrac{\sqrt{320 m n^{-5}}}{\sqrt{45 m-7 n^{3}}}\quad\) b. \(\dfrac{\sqrt[3]{16 x^{4} y^{-2}}}{\sqrt[3]{-54 x^{-2} y^{4}}}\)

    10. a. \(\dfrac{\sqrt{810 c^{-3} d^{7}}}{\sqrt{1000 c d}}\quad\) b. \(\dfrac{\sqrt[3]{24 a^{7} b^{-1}}}{\sqrt[3]{-81 a^{-2} b^{2}}}\)

    11. \(\dfrac{\sqrt{56 x^{5} y^{4}}}{\sqrt{2 x y^{3}}}\)

    12. \(\dfrac{\sqrt{72 a^{3} b^{6}}}{\sqrt{3 a b^{3}}}\)

    13. \(\dfrac{\sqrt[3]{48 a^{3} b^{6}}}{\sqrt[3]{3 a^{-1} b^{3}}}\)

    14. \(\dfrac{\sqrt[3]{162 x^{-3} y^{6}}}{\sqrt[3]{2 x^{3} y^{-2}}}\)


    1. a. \(\dfrac{4}{3}\) b. \(\dfrac{4}{3}\)

    3. a. \(\dfrac{10 m^{2}}{7}\) b. \(\dfrac{3}{y}\)

    5. a. \(\dfrac{5}{6 r^{2}}\) b. \(\dfrac{2x}{3}\)

    7. a. \(\dfrac{6 p}{q^{2}}\) b. \(-\dfrac{2 a^{2}}{b}\)

    9. a. \(\dfrac{8 m^{4}}{3 n^{4}}\) b. \(-\dfrac{2 x^{2}}{3 y^{2}}\)

    11. \(4 x^{4} \sqrt{7 y}\)

    13. \(2 a b \sqrt[3]{2 a}\)

    Exercise SET B: Rationalize a One Term Denominator

    In the following exercises, rationalize the denominator.

    15. a. \(\dfrac{10}{\sqrt{6}}\quad\) b. \(\sqrt{\dfrac{4}{27}}\quad\) c. \(\dfrac{10}{\sqrt{5 x}}\)

    16. a. \(\dfrac{8}{\sqrt{3}}\quad\) b. \(\sqrt{\dfrac{7}{40}}\quad\) c. \(\dfrac{8}{\sqrt{2 y}}\)

    17. a. \(\dfrac{6}{\sqrt{7}}\quad\) b. \(\sqrt{\dfrac{8}{45}}\quad\) c. \(\dfrac{12}{\sqrt{3 p}}\)

    18. a. \(\dfrac{4}{\sqrt{5}}\quad\) b. \(\sqrt{\dfrac{27}{80}}\quad\) c. \(\dfrac{18}{\sqrt{6 q}}\)

    19. a. \(\dfrac{1}{\sqrt[3]{5}}\quad\) b. \(\sqrt[3]{\dfrac{5}{24}}\quad\) c. \(\dfrac{4}{\sqrt[3]{36 a}}\)

    20. a. \(\dfrac{1}{\sqrt[3]{3}}\quad\) b. \(\sqrt[3]{\dfrac{5}{32}}\quad\) c. \(\dfrac{7}{\sqrt[3]{49 b}}\)

    21. a. \(\dfrac{1}{\sqrt[3]{11}}\quad\) b. \(\sqrt[3]{\dfrac{7}{54}}\quad\) c. \(\dfrac{3}{\sqrt[3]{3 x^{2}}}\)

    22. a. \(\dfrac{1}{\sqrt[3]{13}}\quad\) b. \(\sqrt[3]{\dfrac{3}{128}}\quad\) c. \(\dfrac{3}{\sqrt[3]{6 y^{2}}}\)

    23. a. \(\dfrac{1}{\sqrt[4]{7}}\quad\) b. \(\sqrt[4]{\dfrac{5}{32}}\quad\) c. \(\dfrac{4}{\sqrt[4]{4 x^{2}}}\)

    24. a. \(\dfrac{1}{\sqrt[4]{4}}\quad\) b. \(\sqrt[4]{\dfrac{9}{32}}\quad\) c. \(\dfrac{6}{\sqrt[4]{9 x^{3}}}\)

    25. a. \(\dfrac{1}{\sqrt[4]{9}}\quad\) b. \(\sqrt[4]{\dfrac{25}{128}}\quad\) c. \(\dfrac{6}{\sqrt[4]{27 a}}\)

    26. a. \(\dfrac{1}{\sqrt[4]{8}}\quad\) b. \(\sqrt[4]{\dfrac{27}{128}}\quad\) c. \(\dfrac{16}{\sqrt[4]{64 b^{2}}}\)


    15. a. \(\dfrac{5 \sqrt{6}}{3}\) b. \(\dfrac{2 \sqrt{3}}{9}\) c. \(\dfrac{2 \sqrt{5 x}}{x}\)

    17. a. \(\dfrac{6 \sqrt{7}}{7}\) b. \(\dfrac{2 \sqrt{10}}{15}\) c. \(\dfrac{4 \sqrt{3 p}}{p}\)

    19. a. \(\dfrac{\sqrt[3]{25}}{5}\) b. \(\dfrac{\sqrt[3]{45}}{6}\) c. \(\dfrac{2 \sqrt[3]{6 a^{2}}}{3 a}\)

    21. a. \(\dfrac{\sqrt[3]{121}}{11}\) b. \(\dfrac{\sqrt[3]{28}}{6}\) c. \(\dfrac{\sqrt[3]{9 x}}{x}\)

    23. a. \(\dfrac{\sqrt[4]{343}}{7}\) b. \(\dfrac{\sqrt[4]{40}}{4}\) c. \(\dfrac{2 \sqrt[4]{4 x^{2}}}{x}\)

    25. a. \(\dfrac{\sqrt[4]{9}}{3}\) b. \(\dfrac{\sqrt[4]{50}}{4}\) c. \(\dfrac{2 \sqrt[4]{3 a^{2}}}{a}\)

    Exercise SET C: Rationalize a Two Term Denominator

    In the following exercises, simplify.

    27. \(\dfrac{8}{1-\sqrt{5}}\)

    28. \(\dfrac{7}{2-\sqrt{6}}\)

    29. \(\dfrac{6}{3-\sqrt{7}}\)

    30. \(\dfrac{5}{4-\sqrt{11}}\)

    31. \(\dfrac{\sqrt{3}}{\sqrt{m}-\sqrt{5}}\)

    32. \(\dfrac{\sqrt{5}}{\sqrt{n}-\sqrt{7}}\)

    33. \(\dfrac{\sqrt{2}}{\sqrt{x}-\sqrt{6}}\)

    34. \(\dfrac{\sqrt{7}}{\sqrt{y}+\sqrt{3}}\)

    35. \(\dfrac{\sqrt{r}+\sqrt{5}}{\sqrt{r}-\sqrt{5}}\)

    36. \(\dfrac{\sqrt{s}-\sqrt{6}}{\sqrt{s}+\sqrt{6}}\)

    37. \(\dfrac{\sqrt{x}+\sqrt{8}}{\sqrt{x}-\sqrt{8}}\)

    38. \(\dfrac{\sqrt{m}-\sqrt{3}}{\sqrt{m}+\sqrt{3}}\)


    27. \(-2(1+\sqrt{5})\)

    29. \(3(3+\sqrt{7})\)

    31. \(\dfrac{\sqrt{3}(\sqrt{m}+\sqrt{5})}{m-5}\)

    33. \(\dfrac{\sqrt{2}(\sqrt{x}+\sqrt{6})}{x-6}\)

    35. \(\dfrac{(\sqrt{r}+\sqrt{5})^{2}}{r-5}\)

    37. \(\dfrac{(\sqrt{x}+2 \sqrt{2})^{2}}{x-8}\)

    Exercise SET D: writing exercises

      1. Simplify \(\sqrt{\dfrac{27}{3}}\) and explain all your steps.
      2. Simplify \(\sqrt{\dfrac{27}{5}}\) and explain all your steps.
      3. Why are the two methods of simplifying square roots different?
    1. Explain what is meant by the word rationalize in the phrase, "rationalize a denominator."
    2. Explain why multiplying \(\sqrt{2x}-3\) by its conjugate results in an epxression with no radicals.
    3. Explain why multiplying \(\dfrac{7}{\sqrt[3]{x}}\) by \(\dfrac{\sqrt[3]{x}}{\sqrt[3]{x}}\) does not rationalize the denominator.

    1. Answers will vary

    3. Answers will vary

    Self Check

    a. After completing the exercises, use this checklist to evaluate your mastery of the objectives of this section.

    This table has 4 rows and 4 columns. The first row is a header row and it labels each column. The first column header is “I can…”, the second is “Confidently”, the third is “With some help”, and the fourth is “No, I don’t get it”. Under the first column are the phrases “divide radical expressions.”, “rationalize a one term denominator”, and “rationalize a two term denominator”. The other columns are left blank so that the learner may indicate their mastery level for each topic.
    Figure 8.5.63

    b. After looking at the checklist, do you think you are well-prepared for the next section? Why or why not?