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Prove that the least focal chord of a pa...

Prove that the least focal chord of a parabola is the latus rectum .

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Clearly, `overline(PQ)` is least when `(t-(1)/(t))^(2)` is least i.e. when `(t-(1)/(t))^(2)=0 [because" " "t is real". ]` . Therefore, the least value of `overline(PQ)` is 4a , which is the latus rectum of the parabola (1)
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