Multiply Square Roots: Solving √5 × √5

Square Root Multiplication with Identical Radicands

Solve the following exercise:

55= \sqrt{5}\cdot\sqrt{5}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's solve this problem together.
00:09 When you multiply the square root of one number by the square root of another,
00:14 you get the square root of the product of these numbers.
00:18 Let's apply this formula to our exercise.
00:22 First, calculate the product of the numbers.
00:26 And that's how you find the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following exercise:

55= \sqrt{5}\cdot\sqrt{5}=

2

Step-by-step solution

In order to simplify the given expression, we will use two laws of exponents:

a. The definition of root as an exponent:

an=a1n \sqrt[n]{a}=a^{\frac{1}{n}} b. The law of exponents for multiplication between terms with identical bases:

aman=am+n a^m\cdot a^n=a^{m+n}

Let's start by converting the square roots to exponents using the law mentioned in a:

55=512512= \sqrt{5}\cdot\sqrt{5}= \\ \downarrow\\ 5^{\frac{1}{2}}\cdot5^{\frac{1}{2}}= We'll continue, since we are multiplying two terms with identical bases - we'll use the law of exponents mentioned in b:

512512=512+12=51=5 5^{\frac{1}{2}}\cdot5^{\frac{1}{2}}= \\ 5^{\frac{1}{2}+\frac{1}{2}}=\\ 5^1=\\ \boxed{5} Therefore, the correct answer is answer a.

3

Final Answer

5 5

Key Points to Remember

Essential concepts to master this topic
  • Rule: When multiplying identical square roots, the result equals the radicand
  • Technique: Convert 55 \sqrt{5} \cdot \sqrt{5} to 512512=51=5 5^{\frac{1}{2}} \cdot 5^{\frac{1}{2}} = 5^1 = 5
  • Check: Verify that 5×5=25 5 \times 5 = 25 and 25=5 \sqrt{25} = 5

Common Mistakes

Avoid these frequent errors
  • Adding instead of multiplying the radicands
    Don't think 55=10 \sqrt{5} \cdot \sqrt{5} = \sqrt{10} by adding 5+5! This confuses addition with multiplication rules. Always remember that aa=a \sqrt{a} \cdot \sqrt{a} = a , not 2a \sqrt{2a} .

Practice Quiz

Test your knowledge with interactive questions

Solve the following exercise:

\( \sqrt{\frac{2}{4}}= \)

FAQ

Everything you need to know about this question

Why does 5×5 \sqrt{5} \times \sqrt{5} equal 5 and not 10 \sqrt{10} ?

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Think of it this way: 5 \sqrt{5} means "what number times itself equals 5?" So 5×5 \sqrt{5} \times \sqrt{5} is asking "what number times itself, times itself again?" That's just 5!

Is there a shortcut for multiplying identical square roots?

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Yes! Any square root multiplied by itself always equals the number under the radical. So nn=n \sqrt{n} \cdot \sqrt{n} = n for any positive number n.

What if the square roots are different, like 3×7 \sqrt{3} \times \sqrt{7} ?

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When the radicands are different, you multiply them: 3×7=21 \sqrt{3} \times \sqrt{7} = \sqrt{21} . But when they're identical, like 5×5 \sqrt{5} \times \sqrt{5} , you get just the radicand: 5.

How does the exponent rule work here?

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Converting to exponents helps! 5=512 \sqrt{5} = 5^{\frac{1}{2}} , so 5×5=512×512=512+12=51=5 \sqrt{5} \times \sqrt{5} = 5^{\frac{1}{2}} \times 5^{\frac{1}{2}} = 5^{\frac{1}{2} + \frac{1}{2}} = 5^1 = 5

Can I check my answer another way?

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Absolutely! Since 52.236 \sqrt{5} \approx 2.236 , multiply: 2.236×2.2365 2.236 \times 2.236 \approx 5 . This confirms our exact answer of 5!

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