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Solve the following exponential equations for x: a) 27^x = 93x−2 b) 32^x+1 = 42x−1 c) 81^x−2 = 93x+1. Also solve: a) 32x+1 - 9^x = 162

Mathematics

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Here are the solutions for the exponential equations:

2. Solve for xx:

a) 27x=93x−227^x = 9^{3x-2}

  1. Express both bases as powers of 3.

    (33)x=(32)3x−2(3^3)^x = (3^2)^{3x-2}
  2. Apply the power rule (am)n=amn(a^m)^n = a^{mn}.

    33x=32(3x−2)3^{3x} = 3^{2(3x-2)} 33x=36x−43^{3x} = 3^{6x-4}
  3. Equate the exponents since the bases are the same.

    3x=6x−43x = 6x-4
  4. Solve for xx.

    4=6x−3x4 = 6x - 3x 4=3x4 = 3x x=43x = \frac{4}{3}

    The solution is x=43\boxed{x = \frac{4}{3}}.

    b) 32x+1=42x−132^{x+1} = 4^{2x-1}

  5. Express both bases as powers of 2.

    (25)x+1=(22)2x−1(2^5)^{x+1} = (2^2)^{2x-1}
  6. Apply the power rule (am)n=amn(a^m)^n = a^{mn}.

    25(x+1)=22(2x−1)2^{5(x+1)} = 2^{2(2x-1)} 25x+5=24x−22^{5x+5} = 2^{4x-2}
  7. Equate the exponents since the bases are the same.

    5x+5=4x−25x+5 = 4x-2
  8. Solve for xx.

    5x−4x=−2−55x - 4x = -2 - 5 x=−7x = -7

    The solution is x=−7\boxed{x = -7}.

    c) 81x−2=93x+181^{x-2} = 9^{3x+1}

  9. Express both bases as powers of 9.

    (92)x−2=93x+1(9^2)^{x-2} = 9^{3x+1}
  10. Apply the power rule (am)n=amn(a^m)^n = a^{mn}.

    92(x−2)=93x+19^{2(x-2)} = 9^{3x+1} 92x−4=93x+19^{2x-4} = 9^{3x+1}
  11. Equate the exponents since the bases are the same.

    2x−4=3x+12x-4 = 3x+1
  12. Solve for xx.

    −4−1=3x−2x-4 - 1 = 3x - 2x −5=x-5 = x

    The solution is x=−5\boxed{x = -5}.

    3. Solve for xx:

    a) 32x+1−9x=1623^{2x+1} - 9^x = 162

  13. Rewrite terms with a common base.

    Note that 9=329 = 3^2.

    32x⋅31−(32)x=1623^{2x} \cdot 3^1 - (3^2)^x = 162 3⋅(3x)2−(3x)2=1623 \cdot (3^x)^2 - (3^x)^2 = 162
  14. Let y=3xy = 3^x.

    Substitute yy into the equation.

    3y2−y2=1623y^2 - y^2 = 162 2y2=1622y^2 = 162
  15. Solve for yy.

    y2=1622y^2 = \frac{162}{2} y2=81y^2 = 81 y=±81y = \pm\sqrt{81} y=±9y = \pm 9
  16. Substitute back y=3xy = 3^x.

    Since 3x3^x must be positive, we take y=9y=9.

    3x=93^x = 9 3x=323^x = 3^2 x=2x = 2

    The solution is x=2\boxed{x = 2}.

    b) 8x+1−23x−1=1208^{x+1} - 2^{3x-1} = 120

  17. Rewrite terms with a common base.

    Note that 8=238 = 2^3.

    (23)x+1−23x−1=120(2^3)^{x+1} - 2^{3x-1} = 120 23(x+1)−23x−1=1202^{3(x+1)} - 2^{3x-1} = 120 23x+3−23x−1=1202^{3x+3} - 2^{3x-1} = 120
  18. Factor out 23x2^{3x} using the rule am+n=am⋅ana^{m+n} = a^m \cdot a^n.

    23x⋅23−23x⋅2−1=1202^{3x} \cdot 2^3 - 2^{3x} \cdot 2^{-1} = 120 23x(23−2−1)=1202^{3x} (2^3 - 2^{-1}) = 120 23x(8−12)=1202^{3x} \left( 8 - \frac{1}{2} \right) = 120
  19. Simplify the expression in the parenthesis.

    23x(162−12)=1202^{3x} \left( \frac{16}{2} - \frac{1}{2} \right) = 120 23x(152)=1202^{3x} \left( \frac{15}{2} \right) = 120
  20. Solve for 23x2^{3x}.

    23x=120⋅2152^{3x} = 120 \cdot \frac{2}{15} 23x=240152^{3x} = \frac{240}{15} 23x=162^{3x} = 16
  21. Express 16 as a power of 2 and solve for xx.

    23x=242^{3x} = 2^4 3x=43x = 4 x=43x = \frac{4}{3}

    The solution is x=43\boxed{x = \frac{4}{3}}.

    c) 72x+1−49x=2947^{2x+1} - 49^x = 294

  22. Rewrite terms with a common base.

    Note that 49=7249 = 7^2.

    72x⋅71−(72)x=2947^{2x} \cdot 7^1 - (7^2)^x = 294 7⋅(7x)2−(7x)2=2947 \cdot (7^x)^2 - (7^x)^2 = 294
  23. Let y=7xy = 7^x.

    Substitute yy into the equation.

    7y2−y2=2947y^2 - y^2 = 294 6y2=2946y^2 = 294
  24. Solve for yy.

    y2=2946y^2 = \frac{294}{6} y2=49y^2 = 49 y=±49y = \pm\sqrt{49} y=±7y = \pm 7
  25. Substitute back y=7xy = 7^x.

    Since 7x7^x must be positive, we take y=7y=7.

    7x=77^x = 7 7x=717^x = 7^1 x=1x = 1

    The solution is x=1\boxed{x = 1}.

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