Multiply Fourth and Seventh Roots: Solving ⁴√8 · ⁷√8

Exponent Laws with Root Multiplication

Solve the following exercise:

8487= \sqrt[4]{8}\cdot\sqrt[7]{8}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:07 Let's simplify this equation.
00:11 Find the C-th root of A raised to the power of B.
00:15 The answer is A to the power of B divided by C.
00:20 Remember, every number is really to the power of one.
00:25 We'll use this idea in our exercise.
00:28 When you multiply numbers with the same base,
00:33 Add the powers to find the power of the result.
00:37 Let's apply this rule and add the powers.
00:42 And there you have it. That's our solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve the following exercise:

8487= \sqrt[4]{8}\cdot\sqrt[7]{8}=

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 multiplication of terms with identical bases:

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

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

8487=814817= \sqrt[\textcolor{red}{4}]{8}\cdot\sqrt[\textcolor{blue}{7}]{8}= \\ \downarrow\\ 8^{\frac{1}{\textcolor{red}{4}}}\cdot8^{\frac{1}{\textcolor{blue}{7}}}=

We continue, since we have a multiplication of two terms with identical bases - we use the law of exponents shown in B:

814817=814+17 8^{\frac{1}{4}}\cdot8^{\frac{1}{7}}= \\ \boxed{8^{\frac{1}{4}+\frac{1}{7}}}

Therefore, the correct answer is answer D.

3

Final Answer

814+17 8^{\frac{1}{4}+\frac{1}{7}}

Key Points to Remember

Essential concepts to master this topic
  • Root to Exponent Rule: Convert an=a1n \sqrt[n]{a} = a^{\frac{1}{n}} before multiplying
  • Same Base Multiplication: 814817=814+17 8^{\frac{1}{4}} \cdot 8^{\frac{1}{7}} = 8^{\frac{1}{4}+\frac{1}{7}}
  • Check: Verify bases are identical before adding exponents ✓

Common Mistakes

Avoid these frequent errors
  • Multiplying the root indices instead of converting to exponents
    Don't multiply 4 × 7 = 28 to get 828 \sqrt[28]{8} ! This ignores proper exponent laws and gives completely wrong results. Always convert roots to fractional exponents first, then add the exponents.

Practice Quiz

Test your knowledge with interactive questions

\( 112^0=\text{?} \)

FAQ

Everything you need to know about this question

Why can't I just multiply the root numbers together?

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Because roots don't multiply that way! Root multiplication requires converting to exponents first. Think of it like this: 84 \sqrt[4]{8} means "what number raised to the 4th power gives 8?" You need exponent laws, not simple multiplication.

How do I remember which exponents to add?

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Remember: when you multiply same bases, you add the exponents. Since both terms have base 8, we add 14+17 \frac{1}{4} + \frac{1}{7} . If the bases were different, you couldn't combine them this way!

Do I need to calculate the final decimal value?

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No! Leave your answer as 814+17 8^{\frac{1}{4}+\frac{1}{7}} . This exact form shows you understand the exponent laws. Converting to decimals often creates rounding errors and loses the mathematical precision.

What if the bases were different numbers?

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If you had something like 84167 \sqrt[4]{8} \cdot \sqrt[7]{16} , you cannot combine them using the same base rule. You'd need to convert both to the same base first (like powers of 2) or calculate each root separately.

Can I simplify the fraction in the exponent?

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You could find a common denominator for 14+17=7+428=1128 \frac{1}{4} + \frac{1}{7} = \frac{7+4}{28} = \frac{11}{28} , but it's not required. The answer 814+17 8^{\frac{1}{4}+\frac{1}{7}} clearly shows your work and is perfectly acceptable!

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