1.Given a circle C with center A and radius r. 2.Given a line D with a vector u passing through point P_0. 3.Knowing that P is on D only if P=P_0+tu 4.Knowing that P is on C if norm(P−A^2)=r^2 Prove that point P is on C and D if there exists a real number t where [norm(u)^2]t^2+[2(P_0-A) * u]t+[norm(P_0-A^2)-r^2]=0 What properties should I be using in order to solve this?

Miguel Mathis

Miguel Mathis

Open question

2022-08-25

1.Given a circle C with center A and radius r.
2.Given a line D with a vector u passing through point P 0 .
3.Knowing that P is on D only if P = P 0 + t u
4.Knowing that P is on C if P A 2 = r 2
Prove that point P is on C and D if there exists a real number t where
[ u 2 ] t 2 + [ 2 ( P 0 A ) u ] t + [ P 0 A 2 r 2 ] = 0.
What properties should I be using in order to solve this?

Answer & Explanation

Willow Avery

Willow Avery

Beginner2022-08-26Added 11 answers

That equation is what we get when we expand out P 0 + t u A 2 = r 2 :
P 0 + t u A 2 = ( t u + P 0 A ) ( t u + P 0 A ) = t 2 u 2 + 2 t u ( P 0 A ) + P 0 A 2
Set that equal to r 2 , rearrange a bit, and there it is.

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