Tangents drawn from (α,beta) to the hyperbola x2a2−y2b2=1 make angle θ1andθ2 with the x-axis.If tanθ1tanθ2=1, then (α2−beta2) =
A
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B
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C
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D
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Solution
The correct option is C Equation of tangent is y=mx+√a2m2−b2 If this tangent passes through (α,β) we get β=mα+√a2m2−b2⇒(β−mα)2=a2m2−b2 ⇒(α2−a2)m2−2αβm+(β2−b2)=0 Now tanθ1,θ2 are the roots of this equation ∴tanθ1.tanθ2=1⇒β2−b2α2−a2=1⇒α2−a2=β2+b2⇒α2−β2=a2+b2