Is each of the following transformation a linear transformation?
? 1. The transformation T defined by T (x1, x2, x3) = (x1, 0, x3)
? 2. The transformation T defined by T(x1, x2) = (4x1 - 2x2, 3|x2|)
? 3. The transformation T defined by T(x1, x2) = (2x1 - 3x2, x1 + 4, 5x2)
? 4. The transformation T defined by T(x1, x2, x3) = (x1, x2, -x3)
? 5. The transformation T defined by T (x1, x2, x3, x4) = 3x1 + 4x3 - 2x4
? 6. The transformation T defined by T (x1, x2, x3) = (1, x2, x3)