Let <math xmlns="http://www.w3.org/1998/Math/MathML"><mfenced open="|" close="|"><mtable><mtr><mtd><mn>1</mn></mtd><mtd><mn>1</mn></mtd><mtd><mn>1</mn></mtd></mtr><mtr><mtd><mn>1</mn></mtd><mtd><mn>2</mn></mtd><mtd><mn>3</mn></mtd></mtr><mtr><mtd><mi>α</mi></mtd><mtd><mi>β</mi></mtd><mtd><mi>γ</mi></mtd></mtr></mtable></mfenced><mo>=</mo><mi>t</mi></math>, where t is an even prime number & α, β, γ are the integral roots of the equation x<sup>3</sup> - 14x<sup>2</sup> + Px - 36 = 0. The value of P is -
Step-by-Step Solution
Key Concept: The determinant evaluates to (γ - β) - (γ - α) + (β - α) = γ - 2β + α = t. Since t is an even prime, t = 2. Given α, β, γ are roots of x^3 - 14x^2 + Px - 36 = 0, we have α + β + γ = 14, αβ + βγ + γα = P, and αβγ = 36. Solving for integers, we find roots 2, 6, 6 (not distinct) or others. Checking the condition α + γ - 2β = 2 and α + β + γ = 14, we get 3β = 12, so β = 4. Then α + γ = 10 and αγ = 36/4 = 9. Roots are 1 and 9. Thus P = αβ + βγ + γα = 4(1+9) + 9 = 49.
Step 1: Evaluate the given determinant.
The given determinant is:
$$ \begin{vmatrix} 1 & 1 & 1 \\ 1 & 2 & 3 \\ \alpha & \beta & \gamma \end{vmatrix} = t $$
We expand the determinant along the first row:
$$ 1(2\gamma - 3\beta) - 1(\gamma - 3\alpha) + 1(\beta - 2\alpha) = t $$
$$ 2\gamma - 3\beta - \gamma + 3\alpha + \beta - 2\alpha = t $$
$$ \alpha - 2\beta + \gamma = t $$
Step 2: Determine the value of $t$.
The problem states that $t$ is an even prime number. The only even prime number is $2$.
Therefore, we set $t=2$.
So, the equation from the determinant evaluation becomes:
$$ \alpha - 2\beta + \gamma = 2 $$
Step 3: Apply Vieta's formulas to the given cubic equation.
The given cubic equation is $x^3 - 14x^2 + Px - 36 = 0$, and its integral roots are $\alpha, \beta, \gamma$.
According to Vieta's formulas for a cubic equation $ax^3 + bx^2 + cx + d = 0$ with roots $r_1, r_2, r_3$:
Sum of roots: $r_1 + r_2 + r_3 = -b/a$
Sum of products of roots taken two at a time: $r_1r_2 + r_2r_3 + r_3r_1 = c/a$
Product of roots: $r_1r_2r_3 = -d/a$
Applying these to the given equation:
$$ \alpha + \beta + \gamma = -(-14)/1 = 14 \quad \text{(Equation 1)} $$
$$ \alpha\beta\gamma = -(-36)/1 = 36 \quad \text{(Equation 2)} $$
$$ \alpha\beta + \beta\gamma + \gamma\alpha = P/1 = P \quad \text{(Equation 3)} $$
Step 4: Solve for $\beta$ using the system of equations.
We have the equation derived from the determinant:
$$ \alpha - 2\beta + \gamma = 2 \quad \text{(Equation 4)} $$
And from Vieta's formulas:
$$ \alpha + \beta + \gamma = 14 \quad \text{(Equation 1)} $$
Subtract Equation 4 from Equation 1:
$$ (\alpha + \beta + \gamma) - (\alpha - 2\beta + \gamma) = 14 - 2 $$
$$ \alpha + \beta + \gamma - \alpha + 2\beta - \gamma = 12 $$
$$ 3\beta = 12 $$
$$ \beta = 4 $$
Step 5: Find the remaining roots $\alpha$ and $\gamma$.
Substitute $\beta = 4$ into Equation 1:
$$ \alpha + 4 + \gamma = 14 $$
$$ \alpha + \gamma = 10 $$
Now substitute $\beta = 4$ into Equation 2:
$$ \alpha(4)\gamma = 36 $$
$$ \alpha\gamma = 9 $$
We now have two equations: $\alpha + \gamma = 10$ and $\alpha\gamma = 9$.
This means $\alpha$ and $\gamma$ are the roots of the quadratic equation $y^2 - (\alpha+\gamma)y + \alpha\gamma = 0$:
$$ y^2 - 10y + 9 = 0 $$
Factoring the quadratic equation:
$$ (y-1)(y-9) = 0 $$
The roots are $y=1$ and $y=9$.
Therefore, the three integral roots of the cubic equation are $1, 4, 9$. We can assign $\alpha=1, \beta=4, \gamma=9$ (or any permutation).
Step 6: Calculate the value of $P$.
From Equation 3, $P = \alpha\beta + \beta\gamma + \gamma\alpha$.
Substitute the values of the roots $1, 4, 9$:
$$ P = (1)(4) + (4)(9) + (9)(1) $$
$$ P = 4 + 36 + 9 $$
$$ P = 49 $$
Step 7: Classify the value of $P$ and select the correct option.
The calculated value of $P$ is $49$.
Let's check the given options:
(A) a rational number: $49$ is a rational number.
(B) a prime number: $49 = 7^2$, so it is not a prime number.
(C) an odd natural number: $49$ is a positive integer not divisible by $2$, making it an odd natural number.
(D) an even natural number: $49$ is not an even natural number.
While $P=49$ is a rational number, option (C) provides a more specific classification.
The final answer is $\boxed{\text{an odd natural number}}$.
Correct Answer: 3