Two Focal Chords of a Parabola and a Parallelogram

Problem

figure

As shown in the figure, let FF be the focus of the parabola y2=4xy^2 = 4x, and let ABAB and CDCD be two chords of the parabola passing through FF. Let PP be the intersection point of lines ACAC and BDBD, and let lines ACAC and BDBD meet the yy-axis at MM and NN respectively.

1. Prove that PP always lies on the directrix of the parabola. 2. Prove that quadrilateral PMFNPMFN is a parallelogram.

Answer

Solution

Difficulty7/10
TopicsParametrization, conic sections, analytic geometry

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