From the point P(α,β), tangents are drawn to the parabola y2=4x, including an angle 45∘ to each other. Then locus of P(α,β) is
A
a circle with centre (–3,0)
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B
an ellipse with centre (–3,0)
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C
a rectangular hypererbola with centre (–3,0)
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D
a rectangular hypererbola with centre (3,0)
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Solution
The correct option is C a rectangular hypererbola with centre (–3,0) Any tangent to y2=4x is y=mx+1m⇒αm2−βm+1=0 (as P(α,β) lies on it)
Here m1+m2=βα and m1m2=1α
Now, tan45∘=∣∣∣m1−m21+m1m2∣∣∣ ∵(m1−m2)2=(m1+m2)2−4m1m2 ∴(βα)2−4α=(1+1α)2 ⇒β2−4α=(α+1)2⇒(α+3)2−β2=8
We have (x+3)2−y2=8, which is a rectangular hypererbola with centre(−3,0)