2. 試決定下列各個線性變換T,何者不是一對一線性變換?
(A) T:R2→R2, T(x,y)=(y,x)
(B) T:R^{2→R2, T(x,y)=(x+y,x-y)
(C) T:R2→R3, T(x,y)= (x,y,x+y)
(D)T:R2→R3, T(x,y)=(x-y,y-x,2x-2y)}