hw hints from wang499
3.1.10 just solving the system of Ax=0. then can get the kernel of A.
3.1.23 T is invertible. From summary 3.1.8'
3.1.34 To describe a subset of R3 as a kernel means to describe it as an intersection of planes.
By inspection, the given line is the intersection of the planes
x+y = 0 and
2x+z = 0.
Then this means the kernel of the linear transformation T.
