An ellipse has major & minor axes of length and 1 respectively, slides along the coordinate axes and always remains confined in the first quadrant. The locus of centre of ellipse is a circle. Find the number of tangents to the director circle of this circle which are normal to ellipse
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Let foci be (x1, y1) and (x2, y2) and centre be (h, k)
2h = x1 + x2 and 2k = y1 + y2
here x1x2 = y1y = b2
SS’ = 2ae
⇒ (x1 – x2)2 + (y1 – y2)2 = 4a2e2
⇒ (x1 + x2)2 + (y1 – y2)2 – 4x1x2 – 4y1y2 = 4(a2 – b2)
⇒ 4h2 + 4k2 = 4(a2 + b2)
⇒ h2 + k2 =
Locus is x2 + y2 = 1 i.e. circle.
Normal to ellipse will be 3x cos θ – 2y cos θ = 5 ....(i)
(i) is tangent to director circle.
Perpendicular distance from centre
= radius of director circle
⇒
9 sec2 θ + 4 cosec2 θ
= 13 + 9 tan2 θ +
maximum value of LHS
no such θ exists.
number of tangents = 0 Ans.
