Réponse:
a) 5×x + (-3)×2x + x×2x
= 5x + (-6x) + 2x²
= 5x -6x +2x²
= 2x² +5x -6x
= 2x² -x
b) 2x×(-2x) + (-x²)×(-2)
= -4x² + 2x²
= -2x²
c) (-3)×x + (-2x)×(+2x) + x²×3
= -3x + (-4x²) + 3x²
= -3x -4x² +3x²
= -3x -x²
= -x² -3x
d) (-3x) × (2-x) + 3×(x² +3)
= -3x × 2 +3x ×x + 3×x² + 3×3
= -6x +3x² +3x² +9
= -6x +6x² +9
= 6x² -6x +9
