A = -3×1 + x×2 + x×1 + 1×2 + 1×1
= -3 +2x +1x +2 +1
= +3×
B = + 2×1 + 2×x - x×1 - x×x - 3×5 + 3×2x
= +2 +2x -1x -x ( au carré ) -15 +6x
= -13 -7x -x (au carré )
C= + 3x×x -3x×1 + x×2x - x×4 - 2×2x + 2×4
= +3x (au carré ) -3x +2x (au carré ) -4x - 4x +8
= 5x (au carré ) -11x +8
Voilà