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Question 5

Let [tex]$x^3 - 2x^2 - x + 2 = 0$[/tex] be a polynomial equation.

a) Find all potential rational solutions using the Rational Root Theorem. Separate multiple solutions with commas if necessary.

b) Find all the distinct, actual rational solutions. Separate multiple solutions with commas if necessary. If no solutions exist, enter "None".


Sagot :

Certainly! Let's solve the polynomial equation step-by-step.

Given polynomial equation:
[tex]\[x^3 - 2x^2 - x + 2 = 0\][/tex]

### Part a) Finding Potential Rational Solutions Using the Rational Root Theorem:
The Rational Root Theorem states that any potential rational root, \( \frac{p}{q} \), of the polynomial \(a_nx^n + a_{n-1}x^{n-1} + \ldots + a_1x + a_0 = 0\) must be such that:
- \(p\) is a factor of the constant term \(a_0\).
- \(q\) is a factor of the leading coefficient \(a_n\).

In this polynomial:
- The constant term \(a_0 = 2\).
- The leading coefficient \(a_n = 1\).

#### Factors of the constant term (\(a_0 = 2\)):
The factors of 2 are \( \pm1, \pm2 \).

#### Factors of the leading coefficient (\(a_n = 1\)):
The factors of 1 are \( \pm1 \).

#### Potential Rational Roots:
The potential rational roots \( \frac{p}{q} \) are given by:
[tex]\[ \frac{\text{factors of } 2}{\text{factors of } 1} \][/tex]

Thus, the potential rational roots are:
[tex]\[ \pm1, \pm2 \][/tex]

So, the potential rational solutions are:
\( -2, -1, 1, 2 \).

### Part b) Finding the Distinct, Actual Rational Solutions:
We need to test each potential rational root in the original polynomial to determine which ones are actual solutions.

Substitute each potential rational root into the polynomial \(x^3 - 2x^2 - x + 2\) to check if they satisfy the equation:

1. For \(x = -2\):
[tex]\[ (-2)^3 - 2(-2)^2 - (-2) + 2 = -8 - 8 + 2 + 2 = -12 \neq 0 \][/tex]
So, \(x = -2\) is not a solution.

2. For \(x = -1\):
[tex]\[ (-1)^3 - 2(-1)^2 - (-1) + 2 = -1 - 2 + 1 + 2 = 0 \][/tex]
So, \(x = -1\) is a solution.

3. For \(x = 1\):
[tex]\[ 1^3 - 2(1)^2 - 1 + 2 = 1 - 2 - 1 + 2 = 0 \][/tex]
So, \(x = 1\) is a solution.

4. For \(x = 2\):
[tex]\[ 2^3 - 2(2)^2 - 2 + 2 = 8 - 8 - 2 + 2 = 0 \][/tex]
So, \(x = 2\) is a solution.

### Conclusion:
The actual rational solutions to the polynomial equation \(x^3 - 2x^2 - x + 2 = 0\) are:

b) [tex]\( -1, 1, 2 \)[/tex].
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