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# The length of a focal chord of the parabola y^{2} = 4ax at a distance b from the vertex is c. Then

- 2a
^{2} = bc
- a
^{3} = b^{2}c
- ac = b
^{2}
- b
^{2}c = 4a^{3}

^{2}= bc^{3}= b^{2}c^{2}^{2}c = 4a^{3}## The correct answer is: b^{2}c = 4a^{3}

### Chord joining two points t_{1} and t_{2} is

(t_{1} + t_{2})y = 2x + 2at_{1}t_{2}

= b... (1)

a (t_{1} – t_{2})2 = c ... (2)

By using (1) and (2), eliminate t_{1} & t_{2}

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