Solving Exponential Equation for x

CAT 2017 Slot 2 · QA · Medium · Exponents & Logarithms

If 9x1/222x2=4x32x39^{x - 1/2} - 2^{2x - 2} = 4^x - 3^{2x - 3}, then xx is

  1. A.

    3/2

  2. B.

    2/5

  3. C.

    3/4

  4. D.

    4/9

Answer

A

Explanation

Simplify the terms: 9x1/2=32x1=32x39^{x - 1/2} = 3^{2x - 1} = \frac{3^{2x}}{3} 32x3=32x273^{2x - 3} = \frac{3^{2x}}{27} 22x2=4x42^{2x - 2} = \frac{4^x}{4}

Rearrange base 3 terms to one side and base 2 terms to the other: 32x1+32x3=4x+22x23^{2x - 1} + 3^{2x - 3} = 4^x + 2^{2x - 2} 32x(13+127)=4x(1+14)3^{2x}\left(\frac{1}{3} + \frac{1}{27}\right) = 4^x\left(1 + \frac{1}{4}\right) 32x(1027)=4x(54)3^{2x}\left(\frac{10}{27}\right) = 4^x\left(\frac{5}{4}\right) 32x4x=54×2710=278\frac{3^{2x}}{4^x} = \frac{5}{4} \times \frac{27}{10} = \frac{27}{8} (94)x=(32)3\left(\frac{9}{4}\right)^x = \left(\frac{3}{2}\right)^3 (32)2x=(32)3    2x=3    x=32\left(\frac{3}{2}\right)^{2x} = \left(\frac{3}{2}\right)^3 \implies 2x = 3 \implies x = \frac{3}{2}.

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