If a chord joining two points whose eccentric angles are α,β cut the major axis of the ellipse x2a2+y2b2=1, at a distance d from the center, then tanα2tanβ2=
A
d+ad−a
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B
d−ad+a
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C
a−da+d
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D
None of these
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Solution
The correct option is Dd−ad+a EquationofchordjoiningP(α)andQ(β)is:xacos(α+β2)+ybsin(α+β2)=cos(α−β2)X−interceptd=acos(α−β2)cos(α+β2)Or,da=cos(α−β2)cos(α+β2)Bycomponendoanddividendoweget:d+ad−a=cos(α−β2)+cos(α+β2)cos(α−β2)−cos(α+β2)Or,d+ad−a=2cos(α2)∗cos(β2)2sin(α2)∗sin(β2)Or,tan(α2)tan(β2)=d−ad+a