Algebra
Polynomial Equations / Roots
GRB_1000_SCQ
Grade Class 12
Question:
If $\alpha_1, \alpha_2, \alpha_3$ and $\alpha_4$ are the roots of the equation $x^4 + (2 - \sqrt{3})x^2 + (2 + \sqrt{3}) = 0$, then the value of $(1 - \alpha_1)(1 - \alpha_2)(1 - \alpha_3)(1 - \alpha_4)$ is equal to:
Step-by-Step Solution
Key Concept: If $\alpha_i$ are roots of $p(x)$, then $\prod(1-\alpha_i) = p(1)$ when the leading coefficient is 1.
Step 1: Identify the polynomial and its relationship to the product.
We are given the polynomial $p(x) = x^4 + (2 - \sqrt{3})x^2 + (2 + \sqrt{3})$ with roots $\alpha_1, \alpha_2, \alpha_3, \alpha_4$. Since these are the roots, we can write:
$$p(x) = (x - \alpha_1)(x - \alpha_2)(x - \alpha_3)(x - \alpha_4)$$
Step 2: Express the desired product in terms of the polynomial.
We need to find $(1 - \alpha_1)(1 - \alpha_2)(1 - \alpha_3)(1 - \alpha_4)$.
Notice that:
$$(1 - \alpha_1)(1 - \alpha_2)(1 - \alpha_3)(1 - \alpha_4) = (-({\alpha_1 - 1}))(-({\alpha_2 - 1}))(-({\alpha_3 - 1}))(-({\alpha_4 - 1}))$$
Since there are 4 negative signs (an even number), they cancel out:
$$(1 - \alpha_1)(1 - \alpha_2)(1 - \alpha_3)(1 - \alpha_4) = (\alpha_1 - 1)(\alpha_2 - 1)(\alpha_3 - 1)(\alpha_4 - 1)$$
This is equivalent to evaluating $p(1)$ because:
$$p(1) = (1 - \alpha_1)(1 - \alpha_2)(1 - \alpha_3)(1 - \alpha_4)$$
Step 3: Evaluate the polynomial at $x = 1$.
Substitute $x = 1$ into $p(x)$:
$$p(1) = (1)^4 + (2 - \sqrt{3})(1)^2 + (2 + \sqrt{3})$$
$$p(1) = 1 + (2 - \sqrt{3}) + (2 + \sqrt{3})$$
Step 4: Simplify the expression.
Combine like terms:
$$p(1) = 1 + 2 - \sqrt{3} + 2 + \sqrt{3}$$
$$p(1) = 1 + 2 + 2 + (-\sqrt{3} + \sqrt{3})$$
$$p(1) = 5 + 0 = 5$$
Step 5: State the final answer.
Therefore, $(1 - \alpha_1)(1 - \alpha_2)(1 - \alpha_3)(1 - \alpha_4) = 5$.
The answer is **Option 4: 5**.
Correct Answer: 4