Maths-
General
Easy
Question
If length of focal chord of y2 = 4ax is λ, then angle between axis of parabola and focal chord is
- ± sin–1
- ± sin–1
- ± tan–1
- None of these
The correct answer is: ± sin–1
Let any point on focal chord is P(h, k)
where h = a + r cos
k = r sin
Put (h, k) in y2 = 4ax
r2 sin2 = 4a (a + r cos )
r1 + r2 =, r1r2 =
Now here length of focal chord is
= |r1| + |r2|
= r1 –r2
=
= 4a/sin2
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