plane can be written as $$\pmatrix{2\\1\\-1}\cdot\pmatrix{x\\y\\z}=1\;.$$ The angle between the direction vector $\pmatrix{-1\\1\\2}$ of the line and the normal vector $\pmatrix{2\\1\\-1}$ of the plane is complementary to the angle between the line and the plane. share | improve this answer answered May 26 at 4:42 joriki 67.6k 2 61 134 That