Given that (log⁡yx)2log⁡xy+64=0\frac{(\log_y x)^2}{\log_x y} + 64 = 0, express yy in terms of xx. Solve the equation log⁡2x+3=2log⁡2(x−1)\log_2 x + 3 = 2\log_2(x - 1).

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Worked solution

5(a)

1. Apply the change of base formula to express the equation in terms of a single logarithmic base.

Using the change of base formula, log⁡xy=1log⁡yx\log_x y = \frac{1}{\log_y x}.
Substitute this into the given equation:
(log⁡yx)21log⁡yx+64=0\frac{(\log_y x)^2}{\frac{1}{\log_y x}} + 64 = 0

2. Simplify the equation and solve for $\log_y x$.

(log⁡yx)3+64=0(\log_y x)^3 + 64 = 0
(log⁡yx)3=−64(\log_y x)^3 = -64
log⁡yx=−4\log_y x = -4

3. Convert the logarithmic equation to exponential form to express $y$ in terms of $x$.

y−4=xy^{-4} = x
y=x−14y = x^{-\frac{1}{4}} (or y=1x4y = \frac{1}{\sqrt[4]{x}})

Answer

y=x−14y = x^{-\frac{1}{4}}

5(b)

1. Express all terms as logarithms with base 2 and apply the power law

log⁡2x+log⁡223=log⁡2(x−1)2\log_2 x + \log_2 2^3 = \log_2(x - 1)^2
log⁡2x+log⁡28=log⁡2(x−1)2\log_2 x + \log_2 8 = \log_2(x - 1)^2

2. Apply the product law of logarithms and equate the arguments

log⁡2(8x)=log⁡2(x−1)2\log_2(8x) = \log_2(x - 1)^2
8x=(x−1)28x = (x - 1)^2

3. Expand and form a quadratic equation

8x=x2−2x+18x = x^2 - 2x + 1
x2−10x+1=0x^2 - 10x + 1 = 0

4. Solve the quadratic equation and reject the invalid root

x=−(−10)±(−10)2−4(1)(1)2(1)x = \frac{-(-10) \pm \sqrt{(-10)^2 - 4(1)(1)}}{2(1)}
x=10±962x = \frac{10 \pm \sqrt{96}}{2}
x=10±462x = \frac{10 \pm 4\sqrt{6}}{2}
x=5±26x = 5 \pm 2\sqrt{6}

For log⁡2(x−1)\log_2(x - 1) to be defined, x>1x > 1.
Since 5−26≈0.101<15 - 2\sqrt{6} \approx 0.101 < 1, we reject x=5−26x = 5 - 2\sqrt{6}.
Therefore, x=5+26x = 5 + 2\sqrt{6}.

Answer

x=5+26x = 5 + 2\sqrt{6}

AI analysis — may contain mistakes.

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