Evaluate the Fraction: Finding 1/(-2)^7 Step by Step

Negative Exponents with Fractional Forms

1(2)7=? \frac{1}{(-2)^7}=?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:08 Let's simplify this problem together.
00:11 One divided by a number, A, raised to the power of N.
00:16 This equals the base, A, to the power of negative N.
00:21 Let's use this formula in our exercise step by step.
00:27 First, split negative two into factors: negative one and two.
00:37 Remember, if a product is raised to a power, each factor is also raised to that power.
00:43 Now, apply this rule to our exercise.
00:51 You'll find that we're left with a minus.
00:55 And that's how we solve this problem!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

1(2)7=? \frac{1}{(-2)^7}=?

2

Step-by-step solution

To begin with we deal with the expression in the denominator of the fraction. Making note of the power rule for exponents (raising an exponent to another exponent):

(am)n=amn (a^m)^n=a^{m\cdot n} We obtain the following:

(2)7=(12)7=(1)727=127=27 (-2)^7=(-1\cdot2)^7=(-1)^7\cdot2^7=-1\cdot2^7=-2^7

We then return to the initial problem and apply the above information:

1(2)7=127=11127=127 \frac{1}{(-2)^7}=\frac{1}{-2^7}=\frac{1}{-1}\cdot\frac{1}{2^7}=-\frac{1}{2^7}

In the last step we remember that:

11=1 \frac{1}{-1}=-1

Next, we remember the Negative Exponent rule ( raising exponents to a negative power)

an=1an a^{-n}=\frac{1}{a^n} We apply it to the expression we obtained in the last step:

127=27 -\frac{1}{2^7}=-2^{-7} Let's summarize the steps of the solution:

1(2)7=127=27 \frac{1}{(-2)^7}=-\frac{1}{2^7} = -2^{-7}

Therefore, the correct answer is option C.

3

Final Answer

(2)7 (-2)^{-7}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Negative base to odd power equals negative result
  • Technique: Apply negative exponent rule: an=1an a^{-n} = \frac{1}{a^n}
  • Check: Verify answer form matches original expression pattern ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting the negative sign when evaluating odd powers
    Don't treat (-2)^7 as positive 2^7 = wrong sign! Odd powers of negative bases stay negative. Always remember (-2)^7 = -128, so 1/(-2)^7 becomes negative.

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 is (-2)^7 negative but not (-2)^6?

+

The sign depends on whether the exponent is odd or even. Odd powers of negative numbers stay negative, while even powers become positive. So (-2)^7 = -128 but (-2)^6 = +64.

How do I know which answer form is correct?

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Look for the form that shows the same base and operations as the original. Since we started with (-2)^7, the answer (2)7 (-2)^{-7} keeps the same base structure.

Can I simplify (-2)^{-7} further?

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You could write it as 1128 -\frac{1}{128} , but (2)7 (-2)^{-7} is the most compact form that clearly shows the relationship to the original expression.

What's the difference between (-2)^{-7} and -(2^{-7})?

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They're the same! Both equal 1128 -\frac{1}{128} . The negative sign can be written as part of the base (-2) or factored out front of the expression.

Why not choose 2^{-7} as the answer?

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Because 27=1128 2^{-7} = \frac{1}{128} is positive, but our original expression 1(2)7 \frac{1}{(-2)^7} equals a negative value. The signs must match!

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