Maths-
General
Easy
Question
AB is a chord of the parabola y2 = 4ax with vertex at A. BC is drawn perpendicular to AB meeting the axis at C. The projection of BC on the x-axis is-
- a
- 2a
- 4a
- 8a
The correct answer is: 4a
Let B be (at2, 2at)
Slope of AB =
.
Equation of BC is y – 2at = – 
(x – at2).
This meets y = 0 at C whose x-coordinate = 4a + at2
D = (at2, 0)
DC = 4a + at2 – at2 = 4a.
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