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Let F1(x1,0)" and "F2(x2,0), for x1 lt 0...

Let `F_1(x_1,0)" and "F_2(x_2,0)`, for `x_1 lt 0 " and" x_2 gt 0`, be the foci of the ellipse `(x^2)/(9)+(y^2)/(8)=1`. Suppose a parabola having vertex at the origin and focus at `F_2` intersects the ellipse at point M in the first quadrant and at point N in the fourth quadrant.
If the tangents to the ellipse at M and N meet at R and the normal to the parabola at M meets the x-axis at Q, then the ratio of the area of the triangle MQR to area of the quadrilateral `MF_1NF_2` is :

A

`3 : 4`

B

`4 : 5`

C

`5 : 8`

D

`2 : 3`

Text Solution

AI Generated Solution

The correct Answer is:
To solve the problem step by step, we will follow the outlined approach: ### Step 1: Identify the foci of the ellipse The given ellipse is \(\frac{x^2}{9} + \frac{y^2}{8} = 1\). The foci of an ellipse are given by the formula \(c = \sqrt{a^2 - b^2}\), where \(a^2 = 9\) and \(b^2 = 8\). - Calculate \(c\): \[ c = \sqrt{9 - 8} = \sqrt{1} = 1 \] Thus, the foci are at \(F_1(-1, 0)\) and \(F_2(1, 0)\). ### Step 2: Find the equation of the parabola The parabola has its vertex at the origin \((0,0)\) and focus at \(F_2(1,0)\). The standard form of a parabola that opens to the right is given by: \[ y^2 = 4px \] where \(p\) is the distance from the vertex to the focus. Here, \(p = 1\), so the equation of the parabola is: \[ y^2 = 4x \] ### Step 3: Find the points of intersection \(M\) and \(N\) To find the intersection points of the ellipse and the parabola, substitute \(y^2 = 4x\) into the ellipse equation: \[ \frac{x^2}{9} + \frac{4x}{8} = 1 \] This simplifies to: \[ \frac{x^2}{9} + \frac{x}{2} - 1 = 0 \] Multiply through by 18 to eliminate the denominators: \[ 2x^2 + 9x - 18 = 0 \] Now, use the quadratic formula \(x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}\): - Here, \(a = 2\), \(b = 9\), and \(c = -18\). - Calculate the discriminant: \[ D = 9^2 - 4 \cdot 2 \cdot (-18) = 81 + 144 = 225 \] - Now, find the roots: \[ x = \frac{-9 \pm 15}{4} \] This gives: \[ x_1 = \frac{6}{4} = \frac{3}{2}, \quad x_2 = \frac{-24}{4} = -6 \] Since \(M\) is in the first quadrant and \(N\) in the fourth quadrant, we take: \[ M\left(\frac{3}{2}, \sqrt{6}\right), \quad N\left(-6, -\sqrt{24}\right) \] ### Step 4: Find the coordinates of point \(R\) The tangents at points \(M\) and \(N\) can be found using the tangent line equation for the ellipse: \[ \frac{x x_1}{9} + \frac{y y_1}{8} = 1 \] For point \(M\): \[ \frac{x \cdot \frac{3}{2}}{9} + \frac{y \cdot \sqrt{6}}{8} = 1 \] Set \(y = 0\) to find \(R\): \[ \frac{x \cdot \frac{3}{2}}{9} = 1 \implies x = 6 \implies R(6, 0) \] ### Step 5: Find the coordinates of point \(Q\) The normal to the parabola at point \(M\) can be found using the normal line equation: \[ y - y_1 = -\frac{1}{2} (x - x_1) \] Substituting \(M\): \[ y - \sqrt{6} = -\frac{1}{2} \left(x - \frac{3}{2}\right) \] Set \(y = 0\) to find \(Q\): \[ 0 - \sqrt{6} = -\frac{1}{2} \left(x - \frac{3}{2}\right) \] Solving gives: \[ x = \frac{7}{2} \implies Q\left(\frac{7}{2}, 0\right) \] ### Step 6: Calculate the areas 1. **Area of triangle \(MQR\)**: \[ \text{Area} = \frac{1}{2} \times \text{base} \times \text{height} = \frac{1}{2} \times \left(6 - \frac{7}{2}\right) \times \sqrt{6} = \frac{1}{2} \times \frac{5}{2} \times \sqrt{6} = \frac{5\sqrt{6}}{4} \] 2. **Area of quadrilateral \(MF_1NF_2\)**: This can be calculated as twice the area of triangle \(MF_1N\): \[ \text{Area} = 2 \times \frac{1}{2} \times \text{base} \times \text{height} = 2 \times \frac{1}{2} \times \left(-1 - \frac{3}{2}\right) \times \sqrt{6} = 2 \sqrt{6} \] ### Step 7: Find the ratio of the areas The ratio of the area of triangle \(MQR\) to the area of quadrilateral \(MF_1NF_2\) is: \[ \text{Ratio} = \frac{\frac{5\sqrt{6}}{4}}{2\sqrt{6}} = \frac{5}{8} \] Thus, the final answer is: \[ \text{The ratio of the area of triangle } MQR \text{ to the area of quadrilateral } MF_1NF_2 \text{ is } 5:8. \]
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