Let $\alpha$ and $\beta$ are two roots of the equation $x^2 + px + q = 0$, where $p$ and $q$ are real numbers, and $q \neq 0$. Now suppose another quadratic equation $x^2 + mx + n = 0$ with roots $\alpha + \dfrac{1}{\alpha}$ and $\beta + \dfrac{1}{\beta}$ such that $m + n = 0$. Then the possible integral values in the range of $q$ can be:
Step-by-Step Solution
Key Concept: The key idea here is to systematically apply Vieta's formulas to relate the roots and coefficients of both quadratic equations. Subsequently, the derived condition on the coefficients $m+n=0$ is used to form a quadratic equation in $p$, whose discriminant must be non-negative to ensure that $p$ is a real number, thereby determining the possible range for $q$.
Step 1: Apply Vieta's formulas to the first equation $x^2 + px + q = 0$.
The roots are $\alpha$ and $\beta$.
$$ \alpha + \beta = -p $$
$$ \alpha\beta = q $$
Step 2: Determine the sum of roots for the second equation $x^2 + mx + n = 0$.
The roots are $\alpha + \frac{1}{\alpha}$ and $\beta + \frac{1}{\beta}$.
The sum of these roots is $-m$:
$$ -m = \left(\alpha + \frac{1}{\alpha}\right) + \left(\beta + \frac{1}{\beta}\right) $$
$$ -m = (\alpha+\beta) + \left(\frac{1}{\alpha} + \frac{1}{\beta}\right) $$
$$ -m = (\alpha+\beta) + \frac{\alpha+\beta}{\alpha\beta} $$
Substitute the expressions from Step 1:
$$ -m = -p + \frac{-p}{q} = -p\left(1 + \frac{1}{q}\right) = -p\left(\frac{q+1}{q}\right) $$
Therefore,
$$ m = \frac{p(q+1)}{q} $$
Step 3: Determine the product of roots for the second equation $x^2 + mx + n = 0$.
The product of these roots is $n$:
$$ n = \left(\alpha+\frac{1}{\alpha}\right)\left(\beta+\frac{1}{\beta}\right) $$
$$ n = \alpha\beta + \frac{\alpha}{\beta} + \frac{\beta}{\alpha} + \frac{1}{\alpha\beta} $$
$$ n = \alpha\beta + \frac{\alpha^2+\beta^2}{\alpha\beta} + \frac{1}{\alpha\beta} $$
We know that $\alpha^2+\beta^2 = (\alpha+\beta)^2 - 2\alpha\beta$. Substitute from Step 1:
$$ \alpha^2+\beta^2 = (-p)^2 - 2q = p^2 - 2q $$
Substitute this back into the expression for $n$:
$$ n = q + \frac{p^2-2q}{q} + \frac{1}{q} $$
$$ n = q + \frac{p^2-2q+1}{q} $$
Step 4: Apply the given condition $m+n=0$.
Substitute the expressions for $m$ and $n$ from Step 2 and Step 3:
$$ \frac{p(q+1)}{q} + q + \frac{p^2-2q+1}{q} = 0 $$
Since $q \neq 0$, multiply the entire equation by $q$:
$$ p(q+1) + q^2 + p^2 - 2q + 1 = 0 $$
Rearrange the terms to form a quadratic equation in $p$:
$$ p^2 + p(q+1) + (q^2 - 2q + 1) = 0 $$
Recognize that $q^2 - 2q + 1 = (q-1)^2$:
$$ p^2 + p(q+1) + (q-1)^2 = 0 $$
Step 5: Determine the range of $q$ for which real values of $p$ exist.
For $p$ to be a real number, the discriminant of the quadratic equation in $p$ must be non-negative.
The discriminant $D$ is given by $D = (q+1)^2 - 4(1)(q-1)^2$.
$$ D \geq 0 $$
$$ (q+1)^2 - 4(q-1)^2 \geq 0 $$
Expand the terms:
$$ (q^2+2q+1) - 4(q^2-2q+1) \geq 0 $$
$$ q^2+2q+1 - 4q^2+8q-4 \geq 0 $$
$$ -3q^2+10q-3 \geq 0 $$
Multiply by $-1$ and reverse the inequality sign:
$$ 3q^2-10q+3 \leq 0 $$
Factor the quadratic expression:
$$ (3q-1)(q-3) \leq 0 $$
This inequality holds when $q$ is between the roots $\frac{1}{3}$ and $3$.
$$ \frac{1}{3} \leq q \leq 3 $$
Step 6: Identify the possible integral values of $q$.
The problem states that $q$ is a real number and $q \neq 0$. The derived range $\frac{1}{3} \leq q \leq 3$ satisfies $q \neq 0$.
The integral values of $q$ within this range are $1, 2, 3$.
The problem statement only requires $p$ and $q$ to be real numbers, which is ensured by the discriminant condition. The roots $\alpha$ and $\beta$ of the first equation can be complex, and the roots of the second equation will still be well-defined and satisfy the conditions.
The possible integral values in the range of $q$ are $1, 2, 3$.
Correct Answer: 1, 2