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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 find the absolute value of \( k \) given that the line \( y - 2 = 0 \) is the directrix of the parabola defined by the equation \( x^2 - ky + 32 = 0 \) and that the parabola intersects the circle \( x^2 + y^2 = 8 \) at two real distinct points. ### Step-by-Step Solution: 1. **Identify the Directrix and Standard Form of the Parabola**: The directrix of the parabola is given as \( y = 2 \). The standard form of a parabola that opens upwards or downwards is given by: \[ y = ax^2 + bx + c \] or in vertex form, \( (y - k)^2 = 4p(x - h) \). Rearranging the given parabola equation \( x^2 - ky + 32 = 0 \) gives: \[ ky = x^2 + 32 \quad \Rightarrow \quad y = \frac{x^2}{k} + \frac{32}{k} \] 2. **Determine the Vertex**: The vertex of the parabola can be determined from the equation \( y = \frac{x^2}{k} + \frac{32}{k} \). The vertex occurs at \( x = 0 \): \[ y = \frac{0^2}{k} + \frac{32}{k} = \frac{32}{k} \] Therefore, the vertex is at \( (0, \frac{32}{k}) \). 3. **Find the Focus**: The distance from the vertex to the directrix is given by: \[ \text{Distance} = \left| \frac{32}{k} - 2 \right| \] The focus of the parabola is located at \( (h, k + p) \), where \( p \) is the distance from the vertex to the focus. For a parabola, the distance \( p \) is given by \( \frac{1}{4a} \), where \( a = \frac{1}{k} \): \[ p = \frac{k}{4} \] 4. **Set Up the Equation**: The distance from the vertex to the directrix must equal the distance from the vertex to the focus: \[ \left| \frac{32}{k} - 2 \right| = \frac{k}{4} \] 5. **Solve the Equation**: We can split this into two cases: - Case 1: \( \frac{32}{k} - 2 = \frac{k}{4} \) - Case 2: \( \frac{32}{k} - 2 = -\frac{k}{4} \) **Case 1**: \[ \frac{32}{k} - 2 = \frac{k}{4} \] Multiplying through by \( 4k \): \[ 128 - 8k = k^2 \quad \Rightarrow \quad k^2 + 8k - 128 = 0 \] **Case 2**: \[ \frac{32}{k} - 2 = -\frac{k}{4} \] Multiplying through by \( 4k \): \[ 128 - 8k = -k^2 \quad \Rightarrow \quad k^2 - 8k - 128 = 0 \] 6. **Solve the Quadratic Equations**: For both cases, we can apply the quadratic formula \( k = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \). **From Case 1**: \[ k = \frac{-8 \pm \sqrt{8^2 + 4 \cdot 128}}{2} = \frac{-8 \pm \sqrt{64 + 512}}{2} = \frac{-8 \pm \sqrt{576}}{2} = \frac{-8 \pm 24}{2} \] This gives: \[ k = 8 \quad \text{or} \quad k = -16 \] **From Case 2**: \[ k = \frac{8 \pm \sqrt{(-8)^2 + 4 \cdot 128}}{2} = \frac{8 \pm \sqrt{64 + 512}}{2} = \frac{8 \pm 24}{2} \] This gives: \[ k = 16 \quad \text{or} \quad k = -8 \] 7. **Determine Valid Values of k**: We need to find the absolute values: \[ |k| = 8, 16 \] 8. **Conclusion**: Since the parabola intersects the circle at two distinct points, we need to check which values of \( k \) satisfy this condition. The valid values of \( k \) that allow for two intersections with the circle \( x^2 + y^2 = 8 \) lead us to conclude that the absolute value of \( k \) is: \[ \boxed{8} \]
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