Question

Question on Problem set 4; Part II; Problem 2; part c:

I understand the rest of the problem but cannot understand why you test for orthogonality to find that the tangent vector to the curve of intersection and the tangent planes are parallel.

Can anyone help explain? I can't visualize or understand this solution.

Answer 1

if the tangent vector is perpendicular to the normal vector of the planes then it in parallel to the planes/in the plane