The problem asks to find the value of $a^3 - \frac{1}{a^3}$ given that $a^4 - 27a^2 + 1 = 0$.

AlgebraPolynomial EquationsAlgebraic ManipulationFactoringExponents
2025/4/24

1. Problem Description

The problem asks to find the value of a31a3a^3 - \frac{1}{a^3} given that a427a2+1=0a^4 - 27a^2 + 1 = 0.

2. Solution Steps

We are given a427a2+1=0a^4 - 27a^2 + 1 = 0.
Divide the entire equation by a2a^2:
a227+1a2=0a^2 - 27 + \frac{1}{a^2} = 0
a2+1a2=27a^2 + \frac{1}{a^2} = 27
We want to find a31a3a^3 - \frac{1}{a^3}. We know that
(a1a)2=a22+1a2(a - \frac{1}{a})^2 = a^2 - 2 + \frac{1}{a^2}
Substituting the value of a2+1a2a^2 + \frac{1}{a^2},
(a1a)2=272=25(a - \frac{1}{a})^2 = 27 - 2 = 25
Taking the square root:
a1a=±5a - \frac{1}{a} = \pm 5
Now, we use the formula:
a31a3=(a1a)3+3(a1a)a^3 - \frac{1}{a^3} = (a - \frac{1}{a})^3 + 3(a - \frac{1}{a})
Case 1: a1a=5a - \frac{1}{a} = 5
a31a3=(5)3+3(5)=125+15=140a^3 - \frac{1}{a^3} = (5)^3 + 3(5) = 125 + 15 = 140
Case 2: a1a=5a - \frac{1}{a} = -5
a31a3=(5)3+3(5)=12515=140a^3 - \frac{1}{a^3} = (-5)^3 + 3(-5) = -125 - 15 = -140

3. Final Answer

The value of a31a3a^3 - \frac{1}{a^3} is ±140\pm 140.
Final Answer: The final answer is 140\boxed{140}

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