A=(x-7)²-(x²-4x +4)=x²-14x+49-x²+4x-4=-10x+45
B=-9x(7x-2)+(21x-6)=-63x²+18x+21x-6=-63x²+39x-6
C=(x-3)(x+3)+(4x+3)(x+1)=(x²-9)+(4x²+4x+3x+3)=5x²+7x-6
D=(8x+4)-(x-5)(2x+1)=8x+4-(2x²+x-10x-5)=-2x²+17x+9
E=(x+2)²-(x-3)²=(x²+4x+4)-(x²-6x+9)=10x-5
F=5(2x-1)²-(6x+1)+3x(-2x+1)=5(4x²-4x+1)-6x²+3x=20x²-6x²-20x+3x+5=14x²-17x+5
