A variable straight line of slope intersects the hyperbola at two points. The locus of the point which divides the segment between these points in ratio can be written as where and .
Find .
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Relevant wiki: Locus
Let for a particular line the intersection points be ( t 1 , t 1 1 ) and ( t 2 , t 2 1 ) ∴ t 2 − t 1 t 2 1 − t 1 1 = 4 ⟹ t 1 t 2 = − 4 1 Required point P ≡ ( 3 2 t 1 + t 2 , 3 t 1 2 + t 2 1 )
Substituting t 2 = − 4 t 1 1
P ≡ ( 3 2 t 1 − 4 t 1 1 , 3 t 1 2 − 4 t 1 ) ≡ ( x , y ) 3 x = 2 t 1 − 4 t 1 1 ; 3 y = − 4 t 1 + t 1 2 Eliminating t 1 we get,
2 x + y = 2 t 1 1 . . . [ 1 ] Eliminating t 1 1 we get
8 x + y = 4 t 1 . . . [ 2 ] [ 1 ] × [ 2 ] ⟹ ( 8 x + y ) ( 2 x + y ) = 2 ⟹ 1 6 x 2 + y 2 + 1 0 x y = 2 Thus, answer is 2 4