Find the condition for the line xcosθ+ysinθ=P to be a tangent to the ellipse x2a2+y2b2=1.
A
P2=a2cos2θ+b2sin2θ
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B
P2=a2cos2θ−b2sin2θ
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C
P2=b2cos2θ+a2sin2θ
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D
P2=b2cos2θ−a2sin2θ
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Solution
The correct option is AP2=a2cos2θ+b2sin2θ xcosθ+ysinθ=P y=−cosθxsinθ+Psinθ Condition of tangency is c2=a2m2+b2 ⇒P2sin2θ=a2cos2θsin2θ+b2 ⇒P2=a2cos2θ+b2sin2θ