Distinguishing between Conics from General Equation and Eccentricity
If a circle c...
Question
If a circle cuts a rectangular hyperbola xy=c2 in A,B,C,D and the parameters of these four points be t1,t2,t3 and t4 respectively. Then if the eccentricity of a conic is equal to t1.t2.t3.t4, the conic can't be
A
Circle
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B
Parabola
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C
Ellipse
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D
Hyperbola
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Solution
The correct options are A Circle C Ellipse D Hyperbola Let the general point on the hyperbola be (ct,ct). Let the equation of the circle be x2+y2+2gx+2fy+d=0. Substituting (ct,ct) in the equation of the circle, we get,c2t4+2gct3+dt2+2fct+c2=0 Clearly, we have the product of the roots t1.t2.t3.t4=c2c2=1 Hence e=1⇒ Parabola is the required conic. Hence correct options are A,C,D.