A Mixed Conic Fixed-Point Chord

Problem

Consider the ellipse x25+y24=1\dfrac{x^2}5+\dfrac{y^2}4=1 and the circle x2+y2=1x^2+y^2=1. Let PP be a moving point on the ellipse. A point AA on the ellipse is such that the line APAP passes through M(0,1)M(0,1), and a point BB on the circle is such that the line BPBP passes through N(0,12)N\left(0,\dfrac 12\right), with BB and PP on opposite sides of the yy-axis. Prove that the line ABAB passes through a fixed point.

Answer

Solution

Difficulty8/10
TopicsSubstitution, conic sections, analytic geometry, Vieta's Formulas

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