1.

Show that the locus of the midpoints of chords of a parabola passing through the vertex is in turn a parabola whose latus rectum is half of the latus rectum of the original. 

Answer»

The equation of the chord in terms of its midpoint M(x1, y1) is

S1 = S11

⇒ yy1 - 2a(x + x1) = y12 - 4ax1

yy1 - 2ax = y12 - 2ax1 which passes through (0,0)

y12 - 2ax1 = 0

Hence, the locus of M(x1, y1) is the parabola y2 = 2ax.



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