I've done these questions but I would like them to be checked.

My answer is c).Quote:

Let . Then is an n-th root of unity where n is:

a). 12

b). 7

c). 4

d). 3

My answer is b).Quote:

Suppose that u, v and w are unit vectors in . Then is equal to

a).

b). 20

c). 12

d). 16

My answer is c).Quote:

Let be given by T(x,y)=(x+y,x+y,x+y). The image of T is:

a). A point

b). A line

c). A Plane

d). depends on x and y

Can someone check these please. I think they're right.