If $$ 10^x = \frac{1}{2} $$, then $$ 10^{-8x} = $$ $x$
Aptitude
Surds and Indices
Difficulty: Medium
Choose an option
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A$$ \frac{1}{256} $$
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B16
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C80
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D256
Answer
Correct Answer: 256
Explanation
Concept & Formula
This problem is solved using the "Power of a Power" rule in exponents, which allows us to manipulate the given equation to match the target expression.
$$ (a^m)^n = a^{m \times n} $$
$$ a^{-m} = \frac{1}{a^m} $$
Step-by-Step Solution
* We are given that $$ 10^x = \frac{1}{2} $$.
* We need to find the value of $$ 10^{-8x} $$. We can rewrite this target expression using the power of a power rule:
$$ 10^{-8x} = (10^x)^{-8} $$
* Now, substitute the given value of $$ 10^x $$ into our rewritten expression:
$$ \left(\frac{1}{2}\right)^{-8} $$
* Apply the negative exponent rule to flip the fraction and make the exponent positive:
$$ \left(\frac{2}{1}\right)^8 = 2^8 $$
* Calculate the final value:
$$ 2^8 = 256 $$
Exam Strategy & Shortcut
Instead of trying to solve for $x$ using logarithms (which wastes massive amounts of time), manipulate the base structure. You need $$-8x$$ in the exponent, so immediately raise both sides of the known equation to the power of $$-8$$. The right side becomes $$(1/2)^{-8}$$. Since flipping the fraction negates the exponent, this is simply $$2^8$$. Memorizing powers of 2 up to $$2^{10}$$ ($$1024$$) makes calculating $$2^8 = 256$$ an instantaneous mental step.
Common Pitfall
A frequent trap is ignoring the negative sign in the exponent and simply calculating $$(1/2)^8 = 1/256$$, leading students straight to option (a). Always remember that a negative exponent on a fraction effectively turns it upside down.
Final Answer
**Therefore, the correct answer is 256.**