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GATE 2023 MN – Question 9

General Aptitude · Quantitative Aptitude: Algebra, Geometry and Mensuration · 2 marks · Multiple choice

If $x$ satisfies the equation $4^{8^x}=256$, then $x$ is equal to ______.

  1. $1/2$
  2. $\log_{16}8$
  3. $2/3$
  4. $\log_48$

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Correct answer: (C) $2/3$

Explanation

Write 256 as $4^4$. Equality of powers of base 4 gives $8^x=4$. Now write both sides with base 2: $8^x=2^{3x}$ and $4=2^2$. Therefore $3x=2$, so $x=2/3$, option C. Check: $8^{2/3}=4$, which gives $4^4=256$ in the original equation.

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