B=(x-4)(x+6)
=x*x+x*6-4*x-4*6
=x²+2x-24
C=(a-5)(2a-7)
=a*2a-a*7-5*2a-5*(-7)
=2a²-17a+35
D=(4-x²)(x+3)
=4*x+4*3-x²*x-x²*3
=x(au cube)+3x²+4x+12
E=(3x-2)(5x+1)
=3x*5x+3x*1-2*5x-2*1
=15x²-7x-2
F=(4-2x)(-1-3x)
=4*(-1)+4*(-3x)-2x*(-1)-2x*(-3x)
=6x²-14x-4
G=(x+3)(x+3)
=x*x+x*3+x*3+3*3
=x²+6x+9
H=(2-x)(2-x)
=2*2+2*(-x)-x*2-x*(-x)
=2-4x+x²
