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If the line y - 2 =0 is the directrix...

If the line y - 2 =0 is the directrix of the parabola `x^(2) - ky + 32 =0, k ne 0` and the parabola intersects the circle `x^(2) + y^(2) = 8` at two real distinct points, then the absolute value of k is .

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To solve the problem, we need to analyze the given parabola and circle, and find the absolute value of \( k \) such that the parabola intersects the circle at two distinct points. ### Step-by-Step Solution: 1. **Identify the Directrix**: The directrix of the parabola is given as \( y - 2 = 0 \), which means the directrix is the line \( y = 2 \). 2. **Rewrite the Parabola**: The equation of the parabola is given as: \[ x^2 - ky + 32 = 0 \] Rearranging this, we get: \[ x^2 = ky - 32 \] This can be rewritten in the standard form of a parabola: \[ x^2 = k(y - \frac{32}{k}) \] Here, the vertex of the parabola is at \( (0, \frac{32}{k}) \). 3. **Determine the Value of \( a \)**: From the standard form \( x^2 = 4ay \), we can identify: \[ 4a = k \quad \text{and} \quad y_v = \frac{32}{k} \] The distance from the vertex to the directrix is given by: \[ \text{Distance} = \left| \frac{32}{k} - 2 \right| \] This distance must equal \( \frac{k}{4} \) (the distance from the vertex to the focus). 4. **Set Up the Equation**: Therefore, we have: \[ \left| \frac{32}{k} - 2 \right| = \frac{k}{4} \] 5. **Solve the Absolute Value Equation**: This gives us two cases to consider: - Case 1: \[ \frac{32}{k} - 2 = \frac{k}{4} \] Multiplying through by \( 4k \) (assuming \( k \neq 0 \)): \[ 128 - 8k = k^2 \implies k^2 + 8k - 128 = 0 \] - Case 2: \[ \frac{32}{k} - 2 = -\frac{k}{4} \] Multiplying through by \( 4k \): \[ 128 - 8k = -k^2 \implies k^2 - 8k + 128 = 0 \] 6. **Solve the Quadratic Equations**: For Case 1: \[ k^2 + 8k - 128 = 0 \] Using the quadratic formula: \[ k = \frac{-8 \pm \sqrt{8^2 + 4 \cdot 128}}{2} = \frac{-8 \pm \sqrt{64 + 512}}{2} = \frac{-8 \pm \sqrt{576}}{2} = \frac{-8 \pm 24}{2} \] This gives us: \[ k = 8 \quad \text{or} \quad k = -16 \] For Case 2: \[ k^2 - 8k + 128 = 0 \] The discriminant \( (-8)^2 - 4 \cdot 1 \cdot 128 \) is negative, indicating no real solutions. 7. **Conclusion**: The valid values for \( k \) from Case 1 are \( k = 8 \) and \( k = -16 \). Since we need the absolute value of \( k \): \[ |k| = 16 \] ### Final Answer: The absolute value of \( k \) is \( \boxed{16} \).
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