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**HallsofIvy** The difficulty is that there **is** such a linear transformation! The two vectors (1, -1, 1) and (1, 1, 1) are independent- you can map them into anything. Further, (0, 0, 1) is independent of both so {(1, -1, 1), (1, 1, 1), (0, 0, 1)} is a basis for $\displaystyle R^3$. Define T(0, 0, 1) to be whatever you like, say, T(0, 0, 1)= (0, 0), and, together with the first two equations, you have defined a linear transformation from $\displaystyle R^3$ to $\displaystyle R^2$ such that T(1, -1, 1)= (1, 0) and T(1, 1, 1)= (0,1)