Multiply Square Roots: Finding √10 × √3

Square Root Multiplication with Radical Properties

Solve the following exercise:

103= \sqrt{10}\cdot\sqrt{3}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:07 Let's solve this math problem step by step.
00:10 If you take the square root of number A and multiply it with the square root of number B,
00:15 it equals the square root of their product, which is A times B.
00:20 Try using this formula to solve the exercise by finding the product.
00:25 Great job! That's how we 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:

103= \sqrt{10}\cdot\sqrt{3}=

2

Step-by-step solution

To simplify the given expression, we use two laws of exponents:

A. Defining the root as an exponent:

an=a1n \sqrt[n]{a}=a^{\frac{1}{n}} B. The law of exponents for dividing powers with the same base (in the opposite direction):

xnyn=(xy)n x^n\cdot y^n =(x\cdot y)^n

Let's start by using the law of exponents shown in A:

103=1012312= \sqrt{10}\cdot\sqrt{3}= \\ \downarrow\\ 10^{\frac{1}{2}}\cdot3^{\frac{1}{2}}= We continue, since we have a multiplication between two terms with equal exponents, we can use the law of exponents shown in B and combine them under the same base which is raised to the same exponent:

1012312=(103)12=3012=30 10^{\frac{1}{2}}\cdot3^{\frac{1}{2}}= \\ (10\cdot3)^{\frac{1}{2}}=\\ 30^{\frac{1}{2}}=\\ \boxed{\sqrt{30}} In the last steps, we performed the multiplication of the bases and used the definition of the root as an exponent shown earlier in A (in the opposite direction) to return to the root notation.

Therefore, the correct answer is B.

3

Final Answer

30 \sqrt{30}

Key Points to Remember

Essential concepts to master this topic
  • Rule: ab=ab \sqrt{a} \cdot \sqrt{b} = \sqrt{a \cdot b} when both are positive
  • Technique: 103=103=30 \sqrt{10} \cdot \sqrt{3} = \sqrt{10 \cdot 3} = \sqrt{30}
  • Check: Verify using exponent form: 101/231/2=(103)1/2=301/2 10^{1/2} \cdot 3^{1/2} = (10 \cdot 3)^{1/2} = 30^{1/2}

Common Mistakes

Avoid these frequent errors
  • Adding the numbers under the radicals instead of multiplying
    Don't add the radicands: √10 · √3 ≠ √13! This completely ignores the multiplication rule for radicals and gives a wrong result. Always multiply the numbers under the radicals: √10 · √3 = √(10 × 3) = √30.

Practice Quiz

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Choose the largest value

FAQ

Everything you need to know about this question

Why don't I just multiply 10 × 3 to get 30 as the final answer?

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Great question! When you multiply square roots, the result stays under the radical sign. 103=30 \sqrt{10} \cdot \sqrt{3} = \sqrt{30} , not 30. The answer 30 would mean you're claiming 30=30 \sqrt{30} = 30 , which is false!

Can I always combine square roots by multiplying what's inside?

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Yes, but only when multiplying! The rule ab=ab \sqrt{a} \cdot \sqrt{b} = \sqrt{a \cdot b} works for multiplication. For addition like 10+3 \sqrt{10} + \sqrt{3} , you cannot combine them this way.

Should I try to simplify √30 further?

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Check if 30 has any perfect square factors! Since 30 = 2 × 3 × 5 (all prime factors appear once), there are no perfect squares to factor out. So 30 \sqrt{30} is already in simplest form.

How does this relate to exponent rules?

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Square roots are fractional exponents! 10=101/2 \sqrt{10} = 10^{1/2} and 3=31/2 \sqrt{3} = 3^{1/2} . Using the rule xnyn=(xy)n x^n \cdot y^n = (xy)^n , we get 101/231/2=(103)1/2=301/2=30 10^{1/2} \cdot 3^{1/2} = (10 \cdot 3)^{1/2} = 30^{1/2} = \sqrt{30} .

What if the numbers under the radicals were larger?

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The same rule applies! For example, 508=508=400=20 \sqrt{50} \cdot \sqrt{8} = \sqrt{50 \cdot 8} = \sqrt{400} = 20 . Sometimes the result simplifies to a whole number, but often it stays as a radical.

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