Let G={(x,f(x))∣x lies between 0 and 1}; Let (1,0) belong to G. It is given that tangent vector to G at any point is perpendicular to radius vector at that point. Is G parabola or ellipse?

Samson Kaufman

Samson Kaufman

Answered question

2022-08-11

Let G = { ( x , f ( x ) ) x  lies between  0  and  1 }
Let ( 1 , 0 ) belong to G.
It is given that tangent vector to G at any point is perpendicular to radius vector at that point.
Is G parabola or ellipse?

Answer & Explanation

Nicholas Mathis

Nicholas Mathis

Beginner2022-08-12Added 12 answers

Well, you are given that ( 1 , f ( x ) ) ( x , f ( x ) ) and f ( 1 ) = 0. Thus, x + f ( x ) f ( x ) = 0. We can rewrite this as
d d x f 2 ( x ) = 2 x .
Integrating, we get f 2 ( x ) = x 2 + C and by plugging in f ( 1 ) = 0 we see that C = 1. Thus, f ( x ) = ± 1 x 2 and thus G is (part of) a circle.

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