Simplify 7^x × 7^(-x): Multiplying Exponential Expressions

Exponent Laws with Zero Powers

7x7x=? 7^x\cdot7^{-x}=\text{?}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:05 Let's solve this problem together, step by step.
00:09 When you multiply numbers with the same base, add the exponents together.
00:14 So, our final exponent will be the sum of the original exponents.
00:19 We will use this rule to solve our exercise by adding the exponents.
00:24 Remember, any number to the power of zero is one, as long as the number itself is not zero.
00:30 And that gives us our final answer.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

7x7x=? 7^x\cdot7^{-x}=\text{?}

2

Step-by-step solution

We use the law of exponents to multiply terms with identical bases:

aman=am+n a^m\cdot a^n=a^{m+n} We apply the law to given the problem:

7x7x=7x+(x)=7xx=70 7^x\cdot7^{-x}=7^{x+(-x)}=7^{x-x}=7^0 In the first stage we apply the above power rule and in the following stages we simplify the expression obtained in the exponent,

Subsequently, we use the zero power rule:

X0=1 X^0=1 We obtain:

70=1 7^0=1 Lastly we summarize the solution to the problem.

7x7x=7xx=70=1 7^x\cdot7^{-x}=7^{x-x}=7^0 =1 Therefore, the correct answer is option B.

3

Final Answer

1 1

Key Points to Remember

Essential concepts to master this topic
  • Product Rule: When multiplying same bases, add the exponents together
  • Technique: 7x7x=7x+(x)=70 7^x \cdot 7^{-x} = 7^{x+(-x)} = 7^0
  • Check: Any non-zero number raised to power 0 equals 1 ✓

Common Mistakes

Avoid these frequent errors
  • Adding coefficients instead of exponents
    Don't think 7^x × 7^{-x} = 14^{something}! This treats the bases as coefficients instead of using exponent rules. Always keep the same base and add the exponents: x + (-x) = 0.

Practice Quiz

Test your knowledge with interactive questions

Which of the following is equivalent to \( 100^0 \)?

FAQ

Everything you need to know about this question

Why does any number to the power of 0 equal 1?

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This comes from the pattern of exponents! Look: 73=343 7^3 = 343 , 72=49 7^2 = 49 , 71=7 7^1 = 7 . Each time we decrease the exponent by 1, we divide by 7. So 70=71÷7=1 7^0 = 7^1 ÷ 7 = 1 !

What if the base was different, like 5 or 10?

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The result would still be 1! For any non-zero number: 5x5x=50=1 5^x \cdot 5^{-x} = 5^0 = 1 and 10x10x=100=1 10^x \cdot 10^{-x} = 10^0 = 1 . The zero power rule works for all bases.

Can I simplify this without using the zero power rule?

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Yes! Think of 7x 7^{-x} as 17x \frac{1}{7^x} . Then 7x17x=7x7x=1 7^x \cdot \frac{1}{7^x} = \frac{7^x}{7^x} = 1 . Same result, different approach!

What happens if x = 0 in the original expression?

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If x = 0, then 7070=7070=11=1 7^0 \cdot 7^{-0} = 7^0 \cdot 7^0 = 1 \cdot 1 = 1 . The answer is still 1 regardless of what value x has!

Why do we add exponents when multiplying?

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This comes from repeated multiplication! 7273 7^2 \cdot 7^3 means (77)(777) (7 \cdot 7) \cdot (7 \cdot 7 \cdot 7) which gives us 5 sevens total, so 75 7^5 . That's why 2 + 3 = 5!

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