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Let C : y =x^(2) -3, D : y = kx^(2) be t...

Let `C : y =x^(2) -3, D : y = kx^(2)` be two parabolas and
`L_(1)` : `x= a , L_(2) : x = 1 (a ne 0)` be two straight lines.
IF the line `L_(1)` meets the parabola C at a point B on the line `L_(2)`, other than A, then a may be equal to

A

`A) -3`

B

B)`-2`

C

C) 2

D

D) None of these

Text Solution

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The correct Answer is:
To solve the problem, we need to find the value of \( a \) such that the line \( L_1: x = a \) intersects the parabola \( C: y = x^2 - 3 \) at a point \( B \) which lies on the line \( L_2: x = 1 \). ### Step-by-Step Solution: 1. **Identify the Points of Intersection**: - The line \( L_1 \) intersects the parabola \( C \) at the point \( (a, y_1) \). - The line \( L_2 \) intersects the parabola \( C \) at the point \( (1, y_2) \). 2. **Calculate \( y_2 \)**: - Substitute \( x = 1 \) into the equation of parabola \( C \): \[ y_2 = 1^2 - 3 = 1 - 3 = -2 \] - Thus, the coordinates of point \( B \) are \( (1, -2) \). 3. **Find the Coordinates of Point \( A \)**: - The point \( A \) has coordinates \( (a, y_1) \). - Substitute \( x = a \) into the equation of parabola \( C \): \[ y_1 = a^2 - 3 \] - Therefore, the coordinates of point \( A \) are \( (a, a^2 - 3) \). 4. **Find the Slope of the Tangent at Point \( A \)**: - The derivative of \( y = x^2 - 3 \) gives the slope of the tangent: \[ \frac{dy}{dx} = 2x \] - At point \( A \) where \( x = a \): \[ \text{slope at } A = 2a \] 5. **Find the Slope of the Line \( AB \)**: - The slope of the line \( AB \) connecting points \( A(a, a^2 - 3) \) and \( B(1, -2) \) is given by: \[ \text{slope of } AB = \frac{y_2 - y_1}{x_2 - x_1} = \frac{-2 - (a^2 - 3)}{1 - a} = \frac{-2 - a^2 + 3}{1 - a} = \frac{1 - a^2}{1 - a} \] 6. **Set the Slopes Equal**: - For the tangent at point \( A \) to pass through point \( B \), the slopes must be equal: \[ 2a = \frac{1 - a^2}{1 - a} \] 7. **Cross Multiply and Simplify**: - Cross multiplying gives: \[ 2a(1 - a) = 1 - a^2 \] - Expanding and rearranging: \[ 2a - 2a^2 = 1 - a^2 \] \[ 2a^2 - a + 1 = 0 \] 8. **Solve the Quadratic Equation**: - Rearranging gives: \[ a^2 - a + 1 = 0 \] - Using the quadratic formula \( a = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \): \[ a = \frac{1 \pm \sqrt{(-1)^2 - 4 \cdot 1 \cdot 1}}{2 \cdot 1} = \frac{1 \pm \sqrt{1 - 4}}{2} = \frac{1 \pm \sqrt{-3}}{2} \] 9. **Conclusion**: - Since the discriminant is negative, there are no real solutions for \( a \). Hence, the problem might have constraints or conditions that were not specified.
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