The equation of an ellipse is given by . If the slope of the major axis of this ellipse is and the sum of distances of any variable point on the ellipse from its focii is , evaluate the value of .
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As we can see here , the ellipse with implicit equation A x 2 + B x y + C y 2 + D x + E y + F = 0 is an isometric transformation (translation and rotation) of the ellipse with canonical equation a 2 x 2 + b 2 y 2 = 1 .
For the rotation angle, Θ , it holds the relation Θ = arctan ( B 1 ( C − A − ( A − C ) 2 + B 2 ) ) . Hence, the slope of the major axis is m = tan Θ = B 1 ( C − A − ( A − C ) 2 + B 2 ) .
Using A = 1 4 , B = − 4 , C = 1 1 , D = − 4 4 , E = − 5 8 , F = 7 1 , we find m = 2 .
Furthermore, a = B 2 − 4 A C − 2 ( A E 2 + C D 2 − B D E + ( B 2 − 4 A C ) F ) ( ( A + C ) + ( A − C ) 2 + B 2 ) = 6
Thus, the sum of distances of any variable point on the ellipse from its focii is c = 2 a = 2 6 .
For the answer, m c 2 = 2 × ( 2 6 ) 2 = 4 8 .