Solving for Reciprocal: Calculating (7/8) to the Negative Power

Negative Exponents with Fractional Bases

(78)2=? (\frac{7}{8})^{-2}=\text{?}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:07 Let's simplify this problem.
00:11 First, we need to eliminate any negative exponents.
00:15 So, we'll flip the numerator and the denominator, which makes the exponent positive.
00:20 Let's apply this idea to our exercise now.
00:24 When raising a fraction to a power, raise both the top and the bottom to that power.
00:31 We'll use this formula in our exercise again, step by step.
00:39 Next, let's tackle each exponent separately and then solve.
00:47 And there you have it, that's the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

(78)2=? (\frac{7}{8})^{-2}=\text{?}

2

Step-by-step solution

To solve the problem of evaluating (78)2(\frac{7}{8})^{-2}, we'll proceed with these steps:

  • Step 1: Convert the negative exponent into a positive exponent by taking the reciprocal of the base.
  • Step 2: Evaluate the expression obtained after the conversion.

Now, let's work through each step:

Step 1: Convert the negative exponent to a positive exponent using the reciprocal:
Using the property (ab)n=(ba)n(\frac{a}{b})^{-n} = (\frac{b}{a})^{n}, we have:

(78)2=(87)2 (\frac{7}{8})^{-2} = (\frac{8}{7})^{2}

Step 2: Calculate the positive power:

(87)2=8272=6449(\frac{8}{7})^{2} = \frac{8^2}{7^2} = \frac{64}{49}

Thus, the solution to the problem is:
(78)2=6449 (\frac{7}{8})^{-2} = \frac{64}{49}

Extra step to express 6449\frac{64}{49} as a mixed number:

64÷49=1 64 \div 49 = 1 remainder 1515, so 6449=11549\frac{64}{49} = 1 \frac{15}{49} .

Therefore, the simplified solution to the expression (78)2(\frac{7}{8})^{-2} is 11549 1 \frac{15}{49} .

3

Final Answer

11549 1\frac{15}{49}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Negative exponent means take reciprocal then apply positive exponent
  • Technique: (78)2=(87)2=6449 (\frac{7}{8})^{-2} = (\frac{8}{7})^{2} = \frac{64}{49}
  • Check: Convert to mixed number: 64 ÷ 49 = 1 remainder 15 ✓

Common Mistakes

Avoid these frequent errors
  • Making the entire expression negative
    Don't think (78)2 (\frac{7}{8})^{-2} equals 4964 -\frac{49}{64} ! The negative sign is in the exponent, not the result. Always flip the fraction first, then apply the positive exponent.

Practice Quiz

Test your knowledge with interactive questions

Solve the following problem:

\( 1^3= \)

FAQ

Everything you need to know about this question

Why doesn't the negative exponent make the answer negative?

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The negative exponent tells you to flip the fraction, not make it negative! Think of it as: an=1an a^{-n} = \frac{1}{a^n} . The result can still be positive.

How do I remember to flip the fraction?

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Use this memory trick: "Negative exponent = Reciprocal". So (78)2 (\frac{7}{8})^{-2} becomes (87)2 (\frac{8}{7})^{2} - just flip and make the exponent positive!

Do I need to convert to a mixed number?

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It depends on what the question asks for! 6449 \frac{64}{49} and 11549 1\frac{15}{49} are the same value, just in different forms. Check your answer choices to see which format is expected.

What if the base was a whole number instead of a fraction?

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Same rule applies! For example: 32=132=19 3^{-2} = \frac{1}{3^2} = \frac{1}{9} . The negative exponent always means "take the reciprocal".

Can I use a calculator for this?

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Yes, but be careful with parentheses! Enter it as (7/8)^(-2). However, understanding the steps helps you check if your calculator answer makes sense.

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