
Yefim S. answered 10/27/20
Math Tutor with Experience
Vector <2, - 2, 1> is direction vector of this line. Vector <2, 1, - 2> is normal vector of this plane.
We see that this vectors not parallel, because coordinates not proportional, but this vectors perpendicular because their dot-product <2, - 2, 1> • <2, 1, - 2 > = 4 - 2 - 2 = 0. So given line (l) parallel to given plane (α)