Which of these is NOT a linear transformation?
f(x,y)=(x+2,y)f(x, y) = (x+2, y)f(x,y)=(x+2,y)
f(x,y)=(x+y,x−y)f(x, y) = (x+y, x-y)f(x,y)=(x+y,x−y)
f(x,y)=(3x,3y)f(x, y) = (3x, 3y)f(x,y)=(3x,3y)
f(x,y)=(−y,x)f(x, y) = (-y, x)f(x,y)=(−y,x)