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Question
A circle with centre at the origin and radius equal to a meets the axis of x and A and B. P(α) and Q(β) are two points on this circle so that αβ=2γ, where γ is a constant. The locus of the point of intersection of AP and BQ is
Options:
A .  x2−y2−2aytanγ=a2
B .  x2+y2−2aytanγ=a2
C .  x2+y2+2aytanγ=a2
D .  x2−y2+2aytanγ=a2
Answer: Option B
:
B
A Circle With Centre At The Origin And Radius Equal To A Mee...
Coordinates of A are (–a, 0) and of P are (acosα,asinα)
Equation of AP is y=asinαa(cosα+1)(x+a)y=tan(α2)(x+a)(1)
Similarly equation of BQ = y=asinβa(cosβ1)(xa)y=cot(β2)(xa)(2)
From (1) and (2), tan(α2)=yα+x,tan(β2)=axy
Now αβ=2γ
tanγ=tan(α/2)tan(β/2)(a+x)y+(ax)y=yα+xaxy1+yα+x.axytanγ=tan(α/2)tan(β/2)1+tan(α/2)tan(β/2)=x2+y2a22ayx2+y22aytanγ=a2 which is required locus.

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