What is the Normal Vector to the Surface S at the Points of Intersection?

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Discussion Overview

The discussion revolves around finding the normal vector to the surface defined by the equation 9x² + y² − z² − 2y + 2z = 1 at specific points of intersection with a given line. The focus is on the mathematical methods to determine the normal vector, including derivatives and tangent planes.

Discussion Character

  • Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant suggests computing the derivative of the surface equation with respect to the variables to find the tangent directions, implying that the cross product will yield the normal vector at the intersection points.
  • Another participant proposes calculating the tangent planes at the points of intersection and demonstrating that the line is perpendicular to these planes to establish normalcy.
  • A different participant states that the normal vector to a surface defined by f = 0 can be found using the gradient of f at the given point.
  • The initial poster expresses uncertainty about the next steps after identifying the points of intersection.

Areas of Agreement / Disagreement

Participants present multiple methods for determining the normal vector, indicating a lack of consensus on the preferred approach. The discussion remains unresolved regarding the best method to apply.

Contextual Notes

Participants have not fully explored the implications of their proposed methods, and there may be assumptions regarding the continuity and differentiability of the surface that are not explicitly stated.

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Let S be the surface given by the equation 9x^2 + y^2 − z^2 − 2y + 2z = 1, Show that the straight line r(t) = <1, 1, 1> + t<1, 0, 0> is normal to the surface S at the points of intersection.

I set both equations equal to each other and I found their points of intersection are (1/3,1,1) and (-1/3,1,1). But I don't know where to go from there. :confused:
 
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Compute the derivative of the equ. of the surface with respect to the variables. Those are the tengential directions, the cross product is hence giving the normal at a given point...then it should be easy
 
Or compute the tangent planes at the points of intersection and show the line is perpendicular to the planes.
 
the normal vector to a surface f= 0 is the gradient of f at the given point.
 

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