5. Two of the following transformations of vectors in R2 can be performed using a 2x2 transformation matrix, and two cannot. For each transformation below, identify which transformations are possible with a 2x2 matrix (and find those matrices), or explain why it is not a linear transformation.
a) The transformation of R2 that reflects vectors through the line y = 2.
b) The transformation of R2 that rotates vectors 90 degrees counterclockwise and stretches them by a factor of 2 in the horizontal direction.
c) The transformation of R2 that moves all vectors up by 6 units and then shifts them left by 3 units.
d) The transformation of R2 that projects vectors onto the vertical axis.