Bonjour,
8x+20 +5 x² -7x -15x +21
= 5x² -14x +41
4x²` -12x +9 - ( 4x² -12x +x -3)
= 4x²` -12x +9 - 4x² +12x -x +3
= -x +12
x² +5x -3x -15 - ( -3x²+15x +2x -10)
= x² +5x -3x -15 +3x²-15x -2x +10
= 4x² -15x -5
