Let be a given parabola. Let a variable chord cut parabola at points and . Also let be the vertex of the parabola.
Given that locus of intersection of tangents at and is . Let minimum area of of triangle be .
Find the value of .
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Let the points P & Q be ( a t 1 2 , 2 a t 1 ) & ( a t 2 2 , 2 a t 2 ) .
Here a = 4 1 ,
Therefore the points are P ( 4 t 1 2 , 2 t 1 ) & Q ( 4 t 2 2 , 2 t 2 )
So the point of contact of the tangents is ( a t 1 t 2 , a ( t 1 + t 2 ) )
So, point of contact is ( 4 t 1 t 2 , 4 t 1 + t 2 )
As the point of contact lies on the line x + 1 = 0
So t 1 t 2 = − 4
If t 1 = t then t 2 = t − 4
So the points are P ( 4 t 2 , 2 t ) & Q ( t 2 4 , t − 2 )
So the area of the triangle is given by,
2 1 ( ∣ ∣ ∣ ∣ x 1 x 2 y 1 y 2 ∣ ∣ ∣ ∣ + ∣ ∣ ∣ ∣ x 2 x 3 y 2 y 3 ∣ ∣ ∣ ∣ + ∣ ∣ ∣ ∣ x 3 x 1 y 3 y 1 ∣ ∣ ∣ ∣ )
So by substituting the values we get,
Area = t 1 + 4 t
So area is maximum when t = 2 .
So the area is equal to 1 .
So 4 M = 4