If $\alpha$ is the root of the equation $x^2 - x + 2 = 0$ then the value of $\dfrac{6(-\alpha^3 + 2\alpha^2 - \alpha)}{\alpha^5 - 3\alpha^4 + 3\alpha^3 - \alpha^2}$ is equal to:
Step-by-Step Solution
Key Concept: Using roots of polynomial equations to simplify expressions
Step 1: Use the given equation to establish a key relationship.
Since $\alpha$ is a root of $x^2 - x + 2 = 0$, we have:
$$\alpha^2 - \alpha + 2 = 0$$
This gives us the important relation:
$$\alpha^2 = \alpha - 2$$
Step 2: Simplify the numerator using the relation from Step 1.
We need to simplify $-\alpha^3 + 2\alpha^2 - \alpha$.
Factor out $-\alpha$:
$$-\alpha^3 + 2\alpha^2 - \alpha = -\alpha(\alpha^2 - 2\alpha + 1)$$
Recognize that $\alpha^2 - 2\alpha + 1 = (\alpha - 1)^2$:
$$-\alpha^3 + 2\alpha^2 - \alpha = -\alpha(\alpha - 1)^2$$
Step 3: Simplify the denominator using the relation from Step 1.
We need to simplify $\alpha^5 - 3\alpha^4 + 3\alpha^3 - \alpha^2$.
Factor out $\alpha^2$:
$$\alpha^5 - 3\alpha^4 + 3\alpha^3 - \alpha^2 = \alpha^2(\alpha^3 - 3\alpha^2 + 3\alpha - 1)$$
Recognize that $\alpha^3 - 3\alpha^2 + 3\alpha - 1 = (\alpha - 1)^3$ (binomial expansion):
$$\alpha^5 - 3\alpha^4 + 3\alpha^3 - \alpha^2 = \alpha^2(\alpha - 1)^3$$
Step 4: Substitute the simplified numerator and denominator into the original expression.
$$\frac{6(-\alpha^3 + 2\alpha^2 - \alpha)}{\alpha^5 - 3\alpha^4 + 3\alpha^3 - \alpha^2} = \frac{6 \cdot (-\alpha)(\alpha - 1)^2}{\alpha^2(\alpha - 1)^3}$$
Step 5: Cancel common factors.
Cancel $(\alpha - 1)^2$ from numerator and denominator:
$$\frac{6 \cdot (-\alpha)(\alpha - 1)^2}{\alpha^2(\alpha - 1)^3} = \frac{-6\alpha}{\alpha^2(\alpha - 1)}$$
Cancel one factor of $\alpha$:
$$\frac{-6\alpha}{\alpha^2(\alpha - 1)} = \frac{-6}{\alpha(\alpha - 1)}$$
Step 6: Evaluate $\alpha(\alpha - 1)$ using the relation from Step 1.
$$\alpha(\alpha - 1) = \alpha^2 - \alpha$$
Substitute $\alpha^2 = \alpha - 2$:
$$\alpha^2 - \alpha = (\alpha - 2) - \alpha = -2$$
Step 7: Calculate the final value.
$$\frac{-6}{\alpha(\alpha - 1)} = \frac{-6}{-2} = 3$$
**Final Answer:** The value of the given expression is $\boxed{3}$, which corresponds to **Option 1**.
Correct Answer: 3