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(i) Find the exact value of [tex]x[/tex] for which
[tex]\[
\log _2(2 x) = \log _2(5 x + 4) - 3
\][/tex]

(ii) Given that
[tex]\[
\log _a y + 3 \log _a 2 = 5
\][/tex]
express [tex]y[/tex] in terms of [tex]a[/tex]. Give your answer in its simplest form.


Sagot :

Sure, I'll assist you with both parts of the question step by step.

### Part (i)

We need to find the value of [tex]\( x \)[/tex] for the equation:
[tex]\[ \log_2(2x) = \log_2(5x + 4) - 3 \][/tex]

1. First, let's isolate the logarithmic terms on one side:
[tex]\[ \log_2(2x) + 3 = \log_2(5x + 4) \][/tex]

2. Recognize that adding 3 to the logarithm is equivalent to multiplying by [tex]\( 2^3 = 8 \)[/tex] inside the logarithm:
[tex]\[ \log_2(2x) + 3 = \log_2(8 \cdot 2x) \][/tex]

3. Simplify inside the logarithm:
[tex]\[ \log_2(8 \cdot 2x) = \log_2(16x) \][/tex]

4. Now we equate the two logarithms:
[tex]\[ \log_2(16x) = \log_2(5x + 4) \][/tex]

5. Since the logarithms are equal, their arguments must be equal as well:
[tex]\[ 16x = 5x + 4 \][/tex]

6. Solve for [tex]\( x \)[/tex]:
[tex]\[ 16x - 5x = 4 \][/tex]
[tex]\[ 11x = 4 \][/tex]
[tex]\[ x = \frac{4}{11} \][/tex]

So the exact value of [tex]\( x \)[/tex] is [tex]\( \frac{4}{11} \)[/tex].

### Part (ii)

We need to express [tex]\( y \)[/tex] in terms of [tex]\( a \)[/tex] given the equation:
[tex]\[ \log_a y + 3 \log_a 2 = 5 \][/tex]

1. Utilize the logarithmic property [tex]\( \log_b(m^n) = n \log_b m \)[/tex]:
[tex]\[ \log_a y + \log_a (2^3) = 5 \][/tex]

2. Simplify [tex]\( 2^3 \)[/tex]:
[tex]\[ \log_a y + \log_a 8 = 5 \][/tex]

3. Combine the logarithms:
[tex]\[ \log_a (y \cdot 8) = 5 \][/tex]

4. Express the logarithmic equation in exponential form:
[tex]\[ y \cdot 8 = a^5 \][/tex]

5. Solve for [tex]\( y \)[/tex]:
[tex]\[ y = \frac{a^5}{8} \][/tex]

So [tex]\( y \)[/tex] in its simplest form is [tex]\( \frac{a^5}{8} \)[/tex].

### Summary
- For part (i), the exact value of [tex]\( x \)[/tex] is [tex]\( \frac{4}{11} \)[/tex].
- For part (ii), [tex]\( y \)[/tex] expressed in terms of [tex]\( a \)[/tex] is [tex]\( \frac{a^5}{8} \)[/tex].
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