The problem asks to solve the equation $\frac{\log(35-x^3)}{\log(5-x)} = 3$.

AlgebraLogarithmsEquationsQuadratic EquationsExtraneous Solutions
2025/4/23

1. Problem Description

The problem asks to solve the equation log(35x3)log(5x)=3\frac{\log(35-x^3)}{\log(5-x)} = 3.

2. Solution Steps

We are given the equation:
log(35x3)log(5x)=3\frac{\log(35-x^3)}{\log(5-x)} = 3
Using the change of base formula for logarithms, we can rewrite this as:
log5x(35x3)=3\log_{5-x}(35-x^3) = 3
This means that:
(5x)3=35x3(5-x)^3 = 35-x^3
Expanding the left side, we have:
12575x+15x2x3=35x3125 - 75x + 15x^2 - x^3 = 35 - x^3
Simplifying the equation:
12575x+15x2x3+x335=0125 - 75x + 15x^2 - x^3 + x^3 - 35 = 0
15x275x+90=015x^2 - 75x + 90 = 0
Divide by 15:
x25x+6=0x^2 - 5x + 6 = 0
Factoring the quadratic:
(x2)(x3)=0(x-2)(x-3) = 0
Therefore, the possible solutions are x=2x=2 and x=3x=3.
Now, we need to check for extraneous solutions. The logarithm is only defined for positive arguments, and the base must be positive and not equal to

1. Thus:

5x>05-x > 0, which implies x<5x < 5.
5x15-x \neq 1, which implies x4x \neq 4.
35x3>035 - x^3 > 0, which implies x3<35x^3 < 35, or x<3533.27x < \sqrt[3]{35} \approx 3.27.
If x=2x=2, then 5x=52=3>05-x = 5-2 = 3 > 0 and 5x15-x \neq 1. Also 35x3=3523=358=27>035-x^3 = 35 - 2^3 = 35-8 = 27 > 0. Thus, x=2x=2 is a valid solution.
If x=3x=3, then 5x=53=2>05-x = 5-3 = 2 > 0 and 5x15-x \neq 1. Also 35x3=3533=3527=8>035-x^3 = 35 - 3^3 = 35-27 = 8 > 0. Thus, x=3x=3 is a valid solution.

2. Final Answer

The solutions are x=2x=2 and x=3x=3.

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