Bonsoir;
A=(2x-1)(3x+1)
=6x² +2x-3x -1
=6x² -x -1
B=(-x-5)(3x-4)
= -3x² +4x -15x +20
= -3x² -11x +20
C=(7x+3)(6x-2)+(x-7)(-3x+4)
= 42x² -14x +18x -6 -3x² +4x +21x -28
= 39x² +26x -34
D=(6x+5)(x+1)-(3x+1)(4x-1)
= 6x² +6x +5x +5 -( 12x² -3x +4x -1)
= 6x² +6x +5x +5 - 12x² +3x -4x +1
= -6x² +4x +6