Algebra II : Multiplying and Dividing Radicals

Study concepts, example questions & explanations for Algebra II

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Example Questions

Example Question #1 : Multiplying And Dividing Radicals

Multiply and express the answer in the simplest form:

\displaystyle \small \sqrt3(\sqrt4-\sqrt3)

Possible Answers:

\displaystyle \small 4\sqrt3-9

\displaystyle \small \sqrt{12}-\sqrt9

\displaystyle \small 2\sqrt3-3

\displaystyle \small \sqrt7-\sqrt6

Correct answer:

\displaystyle \small 2\sqrt3-3

Explanation:

\displaystyle \small \sqrt3(\sqrt4-\sqrt3)

\displaystyle \small \sqrt{12}-\sqrt9

\displaystyle \small \sqrt{12}=\sqrt4 \times \sqrt3=2\sqrt3

\displaystyle \small \sqrt9=3

\displaystyle \small \sqrt{12}-\sqrt9=2\sqrt3-3

Example Question #2 : Multiplying And Dividing Radicals

\displaystyle \left ( \sqrt{x}+\sqrt{6} \right )\left ( \sqrt{x}-\sqrt{6} \right )

Possible Answers:

\displaystyle x-6

\displaystyle x^{2}-36

\displaystyle x-\sqrt{12}

\displaystyle x-\sqrt{6}

\displaystyle \sqrt{x}-6

Correct answer:

\displaystyle x-6

Explanation:

FOIL with difference of squares.  The multiplying cancels the square roots on both terms.  

Example Question #3 : Multiplying And Dividing Radicals

Simplify. 

\displaystyle \sqrt{36} \times 3\sqrt{36}

Possible Answers:

\displaystyle 18

\displaystyle 4\sqrt{36}

\displaystyle 108

\displaystyle 3\sqrt{36}

Correct answer:

\displaystyle 108

Explanation:

We can solve this by simplifying the radicals first: \displaystyle \sqrt{36} =6

Plugging this into the equation gives us: 

\displaystyle 6 \times3(6)=108

Example Question #2 : Multiplying And Dividing Radicals

Simplify.

\displaystyle 5\sqrt{2} \times4\sqrt{2}

Possible Answers:

\displaystyle 40

\displaystyle 20

\displaystyle \sqrt{80}

\displaystyle 20\sqrt{2}

Correct answer:

\displaystyle 40

Explanation:

Note: the product of the radicals is the same as the radical of the product: 

  which is \displaystyle \sqrt{4} =2

Once we understand this, we can plug it into the equation:

 \displaystyle 5\sqrt{2} \times4\sqrt{2} = 5\times4\times \sqrt{2\times 2}

\displaystyle 5\times4\times2=40

Example Question #2 : Multiplying And Dividing Radicals

Simplify.

\displaystyle \frac{\sqrt{32}}{3\sqrt{16}}

Possible Answers:

\displaystyle \frac{4}{12}

\displaystyle \frac{\sqrt{2}}{3}

\displaystyle \frac{4\sqrt{2}}{12}

\displaystyle \sqrt{2}

Correct answer:

\displaystyle \frac{\sqrt{2}}{3}

Explanation:

We can simplify the radicals:

\displaystyle \sqrt{32} =\sqrt{16\times 2} =4\sqrt{2}     and    \displaystyle \sqrt{16} =4

Plug in the simplifed radicals into the equation:

\displaystyle \frac{4\sqrt{2}}{3\times 4} = \frac{4\sqrt{2}}{12}

\displaystyle \frac{4 \sqrt2}{12}=\frac{\sqrt2}{3}

Example Question #2 : Multiplying And Dividing Radicals

Simplify and rationalize the denominator if needed,

\displaystyle \frac{\sqrt{16}}{4\sqrt{2}}

Possible Answers:

\displaystyle \frac{4}{\sqrt{2}}

\displaystyle \frac{1}{2}

\displaystyle \sqrt{2}

\displaystyle \frac{\sqrt2}{2}

Correct answer:

\displaystyle \frac{\sqrt2}{2}

Explanation:

We can only simplify the radical in the numerator:  \displaystyle \sqrt{16} =4

 

Plugging in the simplifed radical into the equation we get:

\displaystyle \frac{4}{4\sqrt{2}} = \frac{1}{\sqrt{2}}

Note: We simplified further because both the numerator and denominator had a "4" which canceled out. 

Now we want to rationalize the denominator,

\displaystyle \frac{1}{\sqrt2}\bigg(\frac{\sqrt2}{\sqrt2}\bigg)=\frac{\sqrt2}{2}

 

Example Question #2 : Multiplying And Dividing Radicals

Simplify\displaystyle 2x^{2}\cdot x^{5}\cdot 3x^{3}

Possible Answers:

\displaystyle 6x^{30}

\displaystyle 6x^{10}

\displaystyle 6x^{13}

\displaystyle 5x^{30}

\displaystyle 5x^{10}

Correct answer:

\displaystyle 6x^{10}

Explanation:

To simplify, you must use the Law of Exponents.

First you must multiply the coefficients then add the exponents:

\displaystyle 2\cdot3\cdot x^{2+5+3}=6\cdot x^{10}=6x^{10}

Example Question #1 : Multiplying And Dividing Radicals

What is the product of \displaystyle \sqrt{12} and \displaystyle 3\sqrt{6}?

Possible Answers:

\displaystyle 18\sqrt{2}

\displaystyle 12\sqrt{18}

\displaystyle 6\sqrt{18}

\displaystyle 3\sqrt{72}

\displaystyle 9\sqrt{24}

Correct answer:

\displaystyle 18\sqrt{2}

Explanation:

First, simplify \displaystyle \sqrt{12}=\sqrt{4\cdot3} to \displaystyle 2\sqrt{3}.

Then set up the multiplication problem:

 \displaystyle 2\sqrt{3}\cdot 3\sqrt{6}.

Multiply the terms outside of the radical, then the terms under the radical:

 \displaystyle 2\cdot 3\sqrt{3\cdot6} then simplfy: \displaystyle 6\sqrt{18}. 

The radical is still not in its simplest form and must be reduced further: 

\displaystyle 6\sqrt{18}=6\cdot3\sqrt{2}=18\sqrt{2}. This is the radical in its simplest form. 

Example Question #2 : Multiplying And Dividing Radicals

Simplify 

\displaystyle {}\frac{\sqrt{117}}{\sqrt{13}}

Possible Answers:

\displaystyle \sqrt{13}

\displaystyle 3

\displaystyle 3\sqrt{13}

\displaystyle \sqrt9

\displaystyle 3\sqrt9

Correct answer:

\displaystyle 3

Explanation:

To divide the radicals, simply divide the numbers under the radical and leave them under the radical: 

\displaystyle \sqrt{\frac{117}{13}}=\sqrt9 

Then simplify this radical: 

\displaystyle \sqrt9=3.

Example Question #1 : Multiplying And Dividing Radicals

Solve and simplify.

\displaystyle \sqrt{2}\cdot \sqrt{3}

 

Possible Answers:

\displaystyle \sqrt{5}

\displaystyle \sqrt{6}

\displaystyle \sqrt{23}

\displaystyle 6

\displaystyle \sqrt{7}

Correct answer:

\displaystyle \sqrt{6}

Explanation:

When multiplying radicals, just take the values inside the radicand and perfom the operation.

\displaystyle \sqrt{2}\cdot \sqrt{3}=\sqrt{2\cdot 3}=\sqrt{6}

\displaystyle \sqrt{6} can't be reduced so this is the final answer.

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