Calculate 7^(-4): Evaluating Negative Integer Exponents

Negative Exponents with Reciprocal Conversion

74=? 7^{-4}=\text{?}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:04 Let's solve this problem together.
00:07 Using the power laws, a number A raised to the power of negative N
00:12 is the same as one divided by A raised to the power of N.
00:17 So, let's apply this rule: it changes numbers to fractions and back.
00:23 We get one divided by seven raised to the power of four.
00:28 Now, let's solve seven raised to the power of four using these laws.
00:34 And there you go, that's the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

74=? 7^{-4}=\text{?}

2

Step-by-step solution

We must first remind ourselves of the negative exponent rule:

an=1an a^{-n}=\frac{1}{a^n} When applied to given the expression we obtain the following:

74=174=12401 7^{-4}=\frac{1}{7^4}=\frac{1}{2401}

Therefore, the correct answer is option C.

3

Final Answer

12401 \frac{1}{2401}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Negative exponents mean reciprocal: an=1an a^{-n} = \frac{1}{a^n}
  • Technique: Convert 74 7^{-4} to 174 \frac{1}{7^4} , then calculate 74=2401 7^4 = 2401
  • Check: Verify 74×74=70=1 7^{-4} \times 7^4 = 7^0 = 1 using exponent rules ✓

Common Mistakes

Avoid these frequent errors
  • Multiplying base by negative exponent
    Don't calculate 7 × (-4) = -28! Negative exponents don't mean multiply by a negative number. Always flip to reciprocal first: 74=174 7^{-4} = \frac{1}{7^4} , then evaluate the positive exponent.

Practice Quiz

Test your knowledge with interactive questions

Insert the corresponding expression:

\( \left(\frac{1}{20}\right)^{-7}= \)

FAQ

Everything you need to know about this question

Why does a negative exponent make a fraction?

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Think of it as undoing multiplication. Since 74 7^4 means multiply 7 four times, 74 7^{-4} means divide by 7 four times, which gives you 174 \frac{1}{7^4} !

Is 74 7^{-4} the same as (7)4 (-7)^4 ?

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No! 74=12401 7^{-4} = \frac{1}{2401} (positive fraction), but (7)4=2401 (-7)^4 = 2401 (positive whole number). The negative sign affects the exponent, not the base.

How do I calculate 74 7^4 quickly?

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Break it down step by step: 72=49 7^2 = 49 , then 74=49×49=2401 7^4 = 49 \times 49 = 2401 . You can also use 7×7×7×7 7 \times 7 \times 7 \times 7 if you prefer!

Can negative exponents ever give negative answers?

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Only if the base is negative! For example, (3)2=1(3)2=19 (-3)^{-2} = \frac{1}{(-3)^2} = \frac{1}{9} (positive), but (3)3=1(3)3=127=127 (-3)^{-3} = \frac{1}{(-3)^3} = \frac{1}{-27} = -\frac{1}{27} (negative).

What's the easiest way to remember the negative exponent rule?

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Remember: "Negative exponent = Flip it!" Just move the base from numerator to denominator (or vice versa) and make the exponent positive. 74 7^{-4} flips to 174 \frac{1}{7^4} .

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