http://im54.gulfup.com/ZtJZd5.png [Broken] http://im54.gulfup.com/SJgJXh.png [Broken] Till now compared with other subjects that I studied by my self, linear algebra is really the toughest one Anyway, here I found a plane using characteristic eq. which really surprised me since det(M)=1, M is the matrix I've posted. ##-2x+y+z=0## , how is that? a rotation around plane! in which dimension that's possible!, as the book did I took a vector satisfy the plane that's ##(1,1,1)##, then I found ##\theta = π## Everything is correct according to book solution. But I'm not convinced yet! a plane has a lot of vectors in many directions nevertheless we derived the axis of rotation from plane eq.?! that's really weird. Thanks a lot guys.