Répondre :
A= 4(5x-3)-(2x-1)(x+4)
=20x-12-(2x²+8x-x-4)
=20x-12-2x²-8x+x+4
= -2x²+13x-8
B= 3x-x(4x+1)+(-x+2)(5-4x)
=3x-4x²-x-5x+4x²+10-8x
=-11x+10
C=(2x+3)(-2x+7)-(3x-4)(2+5x)
=-4x²+14x-6x+21-(6x+15x²-8-20x)
=-4x²+14x-6x+21-6x-15x²+8+20x
=-19x²+22x+29
=20x-12-(2x²+8x-x-4)
=20x-12-2x²-8x+x+4
= -2x²+13x-8
B= 3x-x(4x+1)+(-x+2)(5-4x)
=3x-4x²-x-5x+4x²+10-8x
=-11x+10
C=(2x+3)(-2x+7)-(3x-4)(2+5x)
=-4x²+14x-6x+21-(6x+15x²-8-20x)
=-4x²+14x-6x+21-6x-15x²+8+20x
=-19x²+22x+29