Answer:
Option D
Explanation:
Plan
(i) P( at2, 2at) is one end point of focal chord of parabola y2=4ax,
then other end point is (at2,−2at)
(ii) Slope of line joining two points (x1,y1) and (x2,y2) is given by y2−y1x2−x1
If PQ is foacl chord, then coordinates of Q will be (at2,−2at)
Now, slope of QR= slope of PK
2ar+2a/tar2−a/t2=2atat2−2a
⇒ r+1/tr2−1/t2=tt2−2
⇒ 1r−1/t=tt2−2
⇒ r−1t=t2−2t=t−2t
⇒ r=t−1t=t2−1t