Ratio, Proportion, Indices, LogarithmMCQPYQ Dec. 22Question 886 of 305
All Questions

If (3)18=(9)x\displaystyle (\sqrt{3})^{18} = (\sqrt{9})^x, find x\displaystyle x?

Options

A18
B9
C8
D19
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Correct Answer

Option b9

All Options:

  • A18
  • B9
  • C8
  • D19

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Detailed Solution & Explanation

Given the equation:
(3)18=(9)x(\sqrt{3})^{18} = (\sqrt{9})^x
Let us simplify both sides of the equation by writing them with base 3\displaystyle 3:
- Left-hand side (LHS):
LHS=(3)18=(312)18=3182=39\text{LHS} = (\sqrt{3})^{18} = \left(3^{\frac{1}{2}}\right)^{18} = 3^{\frac{18}{2}} = 3^9
- Right-hand side (RHS):
Since 9=3\displaystyle \sqrt{9} = 3, we have:
RHS=(9)x=(3)x=3x\text{RHS} = (\sqrt{9})^x = (3)^x = 3^x
Now equate the LHS and RHS:
39=3x3^9 = 3^x
Since the bases are identical, we equate the exponents:
x=9x = 9
This matches **Option B**.
Note: The textbook answer key incorrectly specifies **Option C** (8\displaystyle 8) as correct. However, our rigorous mathematical derivation clearly proves that x=9\displaystyle x = 9 (Option B).
Hence, **Option B** is the correct answer.

About This Chapter: Ratio, Proportion, Indices, Logarithm

Paper

Paper 3: Quantitative Aptitude

Weightage

5-7 Marks

Key Topics

Ratio, Proportion, Indices, Logarithms

This chapter covers Ratio, Proportion, Indices, Logarithms and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 5-7 Marks weightage. Focus on understanding core concepts rather than memorizing.

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