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Let 4x^(2)-4(alpha-2)x + alpha-2=0(alpha...

Let `4x^(2)-4(alpha-2)x + alpha-2=0(alpha in R)` be a quadratic equation. Find the values of `alpha` for which
Both the roots are negative

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To find the values of \( \alpha \) for which both roots of the quadratic equation \( 4x^2 - 4(\alpha - 2)x + \alpha - 2 = 0 \) are negative, we will follow these steps: ### Step 1: Identify the coefficients The given quadratic equation is in the standard form \( ax^2 + bx + c = 0 \) where: - \( a = 4 \) - \( b = -4(\alpha - 2) \) - \( c = \alpha - 2 \) ### Step 2: Ensure the roots are real For the roots to be real, the discriminant \( D \) must be non-negative: \[ D = b^2 - 4ac \geq 0 \] Substituting the values of \( a \), \( b \), and \( c \): \[ D = [-4(\alpha - 2)]^2 - 4(4)(\alpha - 2) \geq 0 \] \[ D = 16(\alpha - 2)^2 - 16(\alpha - 2) \geq 0 \] Factoring out \( 16(\alpha - 2) \): \[ 16(\alpha - 2)[\alpha - 3] \geq 0 \] ### Step 3: Solve the inequality The critical points are \( \alpha = 2 \) and \( \alpha = 3 \). We can test intervals around these points: - For \( \alpha < 2 \): \( 16(\alpha - 2)(\alpha - 3) > 0 \) (both factors negative) - For \( 2 < \alpha < 3 \): \( 16(\alpha - 2)(\alpha - 3) < 0 \) (one factor positive, one negative) - For \( \alpha > 3 \): \( 16(\alpha - 2)(\alpha - 3) > 0 \) (both factors positive) Thus, the solution to the inequality is: \[ \alpha \leq 2 \quad \text{or} \quad \alpha \geq 3 \] ### Step 4: Ensure both roots are negative For both roots to be negative, we need the following conditions: 1. The sum of the roots \( \frac{-b}{a} \) must be positive. 2. The product of the roots \( \frac{c}{a} \) must be positive. **Condition 1: Sum of the roots** \[ \frac{-b}{a} = \frac{4(\alpha - 2)}{4} = \alpha - 2 > 0 \implies \alpha > 2 \] **Condition 2: Product of the roots** \[ \frac{c}{a} = \frac{\alpha - 2}{4} > 0 \implies \alpha - 2 > 0 \implies \alpha > 2 \] ### Step 5: Combine conditions From the conditions derived: - From the discriminant: \( \alpha \leq 2 \) or \( \alpha \geq 3 \) - From the negativity of roots: \( \alpha > 2 \) The only overlapping solution is: \[ \alpha \geq 3 \] ### Final Answer The values of \( \alpha \) for which both roots of the quadratic equation are negative are: \[ \alpha \in [3, \infty) \]
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FIITJEE-QUADRATIC EQUATION & EXPRESSION -ASSIGNMENT PROBLEMS (SUBJECTIVE) Level - II
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