1.

If `P S Q`is a focal chord of the parabola `y^2=8x`such that `S P=6`, then the length of `S Q`is6 (b) 4(c) 3 (d)none of theseA. 6B. 4C. 3D. none of these

Answer» Correct Answer - C
(3) Since the semi-latus rectum of a parabola is the harmonic mean between the segments of any focal chord of the parabola, SP, 4,SQ are in H.P. Therefore,
`4=(2SPxxSQ)/(SP+SQ)`
`or4=(2(6)(SQ))/(6+SQ)`
`or24+4(SQ)=12(SQ)`
`orSQ=3`


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