A Constructed Tangent Line

Problem

The ellipse C:x2a2+y2b2=1C:\dfrac{x^2}{a^2}+\dfrac{y^2}{b^2}=1 (a>b>0a>b>0) has focal distance 44 and passes through the point P(2,3)P\left(\sqrt 2,\sqrt 3\right).

1. Find the equation of the ellipse CC. 2. Let Q(x0,y0)Q(x_0,y_0) (with x0y0≠0x_0y_0\neq 0) be a point on CC. Drop the perpendicular from QQ to the xx-axis, with foot EE. Take A(0,22)A\left(0,2\sqrt 2\right), join AEAE, and draw the line through AA perpendicular to AEAE, meeting the xx-axis at a point DD. Let GG be the reflection of DD across the yy-axis, and draw the line QGQG. Must the line QGQG constructed this way always have exactly one common point with the ellipse CC? Justify your answer.

Answer

Solution

Difficulty7/10
TopicsPole and Polar, conic sections, analytic geometry

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