Math resources Algebra Radicals

Multiplying radicals

Multiplying radicals

Here you will learn all about how to multiply square root expressions (any root expression) and when to simplify the product.

Students first learn how to multiply radicals in algebra and build upon those strategies as they progress through high school math.

What is multiplying radicals?

Multiplying radicals is where you can multiply two or more radical expressions together. Unlike adding radicals, the number under the radical sign does not have to be the same in order to multiply.

When multiplying radical expressions, multiply the coefficients together, the radicands (number under the root symbol) together, and then simplify the expression if necessary.

The strategy of multiplying radical expressions is similar to multiplying algebraic expressions.

Recall multiplying 2a\cdot{3a}. Multiply the coefficients together and the variables together (remember to add exponents when multiplying).

2a\cdot{3a}=6 a^2

To multiply 4a\cdot{9}, multiply the coefficients together. Since only one expression has a variable, remember to bring that down into the answer.

4a\cdot{9}=36a

This strategy can be applied to radical expressions.

Let’s multiply (2\sqrt{3})(3\sqrt{5}). Multiply the whole number coefficients together and the numbers under the radical symbol or square root symbol.

(2\sqrt{3})(3\sqrt{5})=6\sqrt{15}

The number under the radical, 15, cannot be simplified as the largest square number that is a factor of 15 is 1, so leave the answer as is.

Now let’s multiply (7 \sqrt{2})(8). Multiply the whole number coefficients together. Since only one expression has a radical, be sure to include that in the answer.

(7\sqrt{2})(8)=56\sqrt{2}

The number under the radical, 2, cannot be simplified so leave the answer as is.

You can also multiply radical expression binomials using the distributive property, similarly to the way you multiply algebraic expressions.

For example, let’s multiply (2\sqrt{5}-4)(3\sqrt{2}+9)

Using the distributive property, you find the product:

Multiplying radicals 1 US

(2\sqrt{5}-4)(3\sqrt{2}+9)=6\sqrt{10}+18\sqrt{5}-12\sqrt{2}-36

Let’s look at when a radical expression is squared, like in the example of (3 \sqrt{6}+4)^2

When a number or expression is squared it means to multiply it to itself. So, in this case (3 \sqrt{6}+4)^2 means (3 \sqrt{6}+4)(3 \sqrt{6}+4)

Using the distributive property, multiply the expressions together,

Multiplying radicals 3 US

\begin{aligned}(3\sqrt{6}+4)^{2}&=9\sqrt{36}+12\sqrt{6}+12\sqrt{6}+16 \\\\ &=9\times{6}+24\sqrt{6}+16 \\\\ &=70+24\sqrt{6} \end{aligned}

What is multiplying radicals?

What is multiplying radicals?

Common Core State Standards

How does this relate to high school math?

  • High school- The Real Number System (HSN-RN.B.3)
    Explain why the sum or product of two rational numbers is rational; that the sum of a rational number and an irrational number is irrational; and that the product of a nonzero rational number and an irrational number is irrational.

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[FREE] Algebra Worksheet (Grade 6 to 8)

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Use this quiz to check your grade 6 to 8 students’ understanding of algebra. 10+ questions with answers covering a range of 6th and 8th grade algebra topics to identify areas of strength and support!

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How to multiply radicals

In order to multiply radicals:

  1. Multiply the coefficients together and the radicands together.
  2. Simplify the product.

Multiplying radicals examples

Example 1: simplify multiplication

Multiply the radical expressions.

2\sqrt{2}\times{5}\sqrt{3}

  1. Multiply the coefficients together and the radicands together.

Multiply the coefficients together: 2\times{5}=10

Multiply the radicands together: \sqrt{2}\times\sqrt{3}=\sqrt{2\times3}=\sqrt{6}

2Simplify the product.

The product of 2\sqrt{2}\times{5}\sqrt{3}=10\sqrt{6}

10 \sqrt{6} cannot be simplified as the greatest factor that is a square number is 1, so that is the most simplified answer.

Example 2: multiplication with simplifying

Multiply the radical expression.

5\sqrt{3}\times{2}\sqrt{6}

Multiply the coefficients together and the radicands together.

Simplify the product.

Example 3: multiply coefficient of 1

Multiply the radical expression (12\sqrt{6})(\sqrt{8}).

Multiply the coefficients together and the radicands together.

Simplify the product.

Example 4: multiplying radicals using distributive property

Multiply the radical expression \sqrt{2}(4\sqrt{6}-7) .

Multiply the coefficients together and the radicands together.

Simplify the product.

Example 5: multiply using distributive property

Multiply the radical expression (\sqrt{10}+3)(\sqrt{2}-6).

Multiply the coefficients together and the radicands together.

Simplify the product.

Example 6: squaring a radical expression

Simplify the radical expression (\sqrt{11}+5)^2.

Multiply the coefficients together and the radicands together.

Simplify the product.

Teaching tips for multiplying radicals

  • Remind students that there is always a 1 in front of the radical symbol.

  • Instead of assigning worksheets to students, have them practice skills of simplifying radical expressions, multiplying radical expressions, and dividing radical expressions using digital game-play or having students do scavenger hunts around the classroom.

  • Use online tutorials for struggling learners where they can view full videos on step-by-step processes on how to simplify and add radicals.

  • Have students that struggle with math facts, use the square root function on a handheld or digital calculator.

Easy mistakes to make

  • Thinking that you can only multiply radical expressions if the radicals are the same
    Radicals can be multiplied together, whether they are the same or not.

    \sqrt{3}\times\sqrt{3}=\sqrt{9}=3


    \sqrt{5}\times\sqrt{2}=\sqrt{10}

  • Forgetting to simplify each radical fully
    For example, when multiplying, \sqrt{6}\times\sqrt{3}=\sqrt{18}, simplify \sqrt{18} because it has a perfect square factor.

    \begin{aligned}\sqrt{18}&=\sqrt{9\times{2}} \\\\ &=\sqrt{9}\times\sqrt{2} \\\\ &=3\sqrt{2} \end{aligned}

Practice multiplying radicals questions

1. Multiply the radicals, and be sure to simplify the product completely.

 

5\sqrt{2}\times{3}\sqrt{2}

30
GCSE Quiz True

15\sqrt{4}
GCSE Quiz False

8\sqrt{2}
GCSE Quiz False

15
GCSE Quiz False

Multiply the coefficients to each other and the radicands to each other.

 

5\times{3}=15

 

\sqrt{2}\times\sqrt{2}=\sqrt{4}=2

 

Simplify the product.

 

5 \sqrt{2} \times 3 \sqrt{2}=15 \times 2=30

2. Multiply the radical expression, 10\sqrt{2}\times{3}\sqrt{10} .

30\sqrt{12}
GCSE Quiz False

60\sqrt{5}
GCSE Quiz True

30\sqrt{20}
GCSE Quiz False

26\sqrt{5}
GCSE Quiz False

Multiply the coefficients to each other and the radicands to each other.

 

10 \times 3=30

 

\sqrt{2} \times \sqrt{10}=\sqrt{20}

 

\sqrt{20} can be simplified because it has a perfect square factor.

 

\begin {aligned} \sqrt{20}&=\sqrt{4 \times 5} \\\\ &=\sqrt{4} \times \sqrt{5} \\\\ &=2\sqrt{5} \end{aligned}

 

Simplify the product

 

30\times{2}\sqrt{5}=60\sqrt{5}

 

10\sqrt{2}\times{3}\sqrt{10}=60\sqrt{5}

3. Multiply the radical expression and simplify the product.

 

\sqrt{3}(2\sqrt{7}+1)

2\sqrt{10}+\sqrt{3}
GCSE Quiz False

2\sqrt{21}+1
GCSE Quiz False

\sqrt{42}+\sqrt{3}
GCSE Quiz False

2\sqrt{21}+\sqrt{3}
GCSE Quiz True

Multiply using the distributive property.

 

Multiplying radicals 7 US

 

First multiply \sqrt{3}\times{2}\sqrt{7} and then \sqrt{3}\times{1}

 

\sqrt{3}\times{2}\sqrt{7}=2\sqrt{21}

 

\sqrt{3}\times{1}=1\sqrt{3}=\sqrt{3}

 

\sqrt{3}(2\sqrt{7}+1)=2\sqrt{21}+\sqrt{3}

4. Simplify the radical expression – \; \sqrt{5}(4\sqrt{2}+7).

– \; 4\sqrt{10}-7\sqrt{5}
GCSE Quiz True

– \; 4\sqrt{7}-7\sqrt{5}
GCSE Quiz False

4\sqrt{10}+7
GCSE Quiz False

– \; 4\sqrt{10}+7\sqrt{5}
GCSE Quiz False

Use the distributive property to multiply the radical expression.

 

First multiply – \; \sqrt{5}\times{4}\sqrt{2} and then – \; \sqrt{5}\times{7}

 

Multiply coefficients together and radicands together.

 

– \; \sqrt{5}\times{4}\sqrt{2}=- \; 4\sqrt{10}

 

– \; \sqrt{5}\times{7}=- \; 7\sqrt{5}

 

– \; \sqrt{5}(4\sqrt{2}+7)=- \; 4\sqrt{10}-7\sqrt{5}

5. Simplify fully the radical expression (4 \sqrt{2}-3)(\sqrt{5}+6).

4\sqrt{7}-24\sqrt{2}+3\sqrt{5}
GCSE Quiz False

4\sqrt{10}+24\sqrt{2}-3\sqrt{5}-18
GCSE Quiz True

– \; 4\sqrt{10}-24\sqrt{2}+3\sqrt{5}+18
GCSE Quiz False

4\sqrt{10}-24\sqrt{2}-3\sqrt{5}-18
GCSE Quiz False

Use the distributive property to multiply (4 \sqrt{2}-3)(\sqrt{5}+6).

 

(4 \sqrt{2}-3)(\sqrt{5}+6) multiply 4\sqrt{2}\times\sqrt{5} and 4\sqrt{2}\times{6}

 

Multiplying radicals 8 US

 

First, multiply coefficients to each other and radicands to each other.

 

4\sqrt{2}\times\sqrt{5}=4\sqrt{10}

 

4\sqrt{2}\times{6}=24\sqrt{2}

 

– \; 3 \times \sqrt{5}=- \; 3 \sqrt{5}

 

– \; 3 \times 6=- \; 18

 

(4\sqrt{2}-3)(\sqrt{5}+6)=4\sqrt{10}+24\sqrt{2}-3\sqrt{5}-18

6. Square the radical expression (9-\sqrt{7})^2.

18-2\sqrt{7}
GCSE Quiz False

88-18\sqrt{7}
GCSE Quiz True

81+2\sqrt{7}
GCSE Quiz False

81+18\sqrt{7}
GCSE Quiz False
\left(9-\sqrt{7}\right)^2=(9-\sqrt{7})(9-\sqrt{7})

 

Use the distributive property to multiply the expressions together.

 

Multiplying radicals 9 US

 

Multiply coefficients with each other and the radicals with each other.

 

9\times{9}=81

 

9\times(-\sqrt{7})=- \; 9\sqrt{7}

 

– \; \sqrt{7}\times{9}=- \; 9\sqrt{7}

 

– \; \sqrt{7}\times-\sqrt{7}=\sqrt{49}=7

 

\left(9-\sqrt{7}\right)^2=81-9\sqrt{7}-9\sqrt{7}+7

 

You can combine the radicals with ‘like radicals’ so

 

– \; 9\sqrt{7}-9\sqrt{7}=- \; 18\sqrt{7}

 

\left(9-\sqrt{7}\right)^2=81-18\sqrt{7}+7=88-18\sqrt{7}

Multiplying radicals FAQs

Can you multiply cube roots together?

Yes, you can multiply cube roots or any root.

What is the process when dividing radical expressions?

Radical expressions can be divided. You will learn the process on dividing radicals in algebra 1 and algebra 2 or you can go to the “dividing radicals” webpage.

Is the process for solving radical equations the same as for solving quadratic equations?

The process is different. To solve simple radical equations, you need to isolate the radical part to be on one side of the equation. Then apply the correct exponent to both sides of the equation to get rid of the radical sign.

For example, if the root is a cube root, then the exponent or power each side of the equation needs to be raised to is 3.

Can a rational expression contain a radical expression?

Yes, rational expressions are like fractions because they have a numerator and denominator. There can be a radical expression in either the numerator, denominator, or both, but the number value will be irrational.

How do the graphs of polynomial, radical, and exponential functions compare to one another?

The graphs of these functions are quite different. Polynomial functions are smooth curves with no breaks because the domain is all real numbers.

Exponential functions are smooth curves too because the domain is all real numbers but will have a horizontal asymptote. Radical functions are not necessarily classified as being smooth curves because the domain is not all real numbers.

Are functions with rational exponents considered to be radical functions?

Functions or expressions with rational exponents are considered to be radical functions because you can represent a root symbol with a rational exponent.

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