... x4 = 6, 2x1 + 3x2 − 4x3 + 4x4 = 7, 2) 3x1 + x2 − 2x3 − 2x4 = 9, x1 − 3x2 + 7x3 + 6x4 = −7 ´ ’ Giai 1) Ap dung cˆng th´.c (4. 4) o u xj = det(Aj ) , detA j = 1, (4. 7) (4. 8) ’ 4. 1 ... + x4 x1 + x2 − 2x3 − x4 x1 + x2 − 4x3 + 3x4 x1 + x2 + 7x3 + 5x4 = 1, = 0, = 2, = − 3x2 − 2x4 − 2x4 , x3 = , x2 , x4 t`y y) u ´ 3 x1 + 2x2 + 3x3 + 4x4 = 5, x2 + 2x3 + 3x4 ... + 4x4 x1 + x2 + 5x3 + 6x4 = (DS x1 = 10 15 13 , x2 = , x3 = − , x4 = 2) 4 x1 + 2x2 + 3x3 + 4x4 = 30, −x1 + 2x2 − 3x3 + 4x4 = 10, x2 − x3 + x4 = 3, = 10 x1 + x2 + x3 + x4...