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 From a point (sinθ,cosθ) , if three normals can be drawn  to the parabola y2=4ax, then the value of a is 

a
(1/2,1)
b
[−1/2,0)
c
[−1/2,1]
d
(−1/2,0)∪(0,1/2)

detailed solution

Correct option is D

Point (sin⁡θ,cos⁡θ) lies on the circle x2+y2=1∀θ∈R Now, three normals can be drawn to the parabola y2=4ax if x=|2a| meets this circle.  Hence, we must have cos⁡θ>|2a| or 0<|2a|<1 or 0<|a|<12 or a∈−12,0∪0,12

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