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Parallel tangent plane.

  1. Oct 15, 2011 #1
    1. The problem statement, all variables and given/known data
    Find the points on the hyperboloid 9x^2 -45y^2+5z^2 = 45 where the tangent plane is parallel to x+5y-2z = 7.

    2. Relevant equations

    3. The attempt at a solution

    Ok so the tangent plane is parallel to the x+5y-2z=7 when their normal vectors are parallel. So that means that the normal vector for the given plane (1,5,-2) should also be a normal vector for the tangent plane to the hyperboloid.

    So since the equation of the plane can be written as

    (1,5,-2) . (x-x0,y-y0,z-z0) = x - x0 + 5y -5y0 -2z + 2z0 where -x0 - 5y0 +2z0 = -7

    and the equation of the tangent plane to the hyperboloid can be written as the gradient at (x0,y0,z0) . (x-x0,y-y0,z-z0)

    the gradient is (18x0, -90y0, 10z0) at (x0,y0,z0). and it has to be equal to the normal vector (1,5,-2).

    So 18x0 = 1, -90y0 = 5, 10z0 = -2? and then solve for x0,y0,z0 and that is the point I'm looking for?

    Just wanted to know if I'm doing this right.
  2. jcsd
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