Đáp án:
a) (2x-1)(x²+5-4)
=2x³+10x-8x-x²-5+4
=x²+2x-1
b) -(5x-4)(2x+3)
=-(10x²+15x-8x-12)
=-10x²-7x+12
c) (2x-y)(4x²-2xy+y²)
=8x³+4x²y-2xy²-4x²y+2x²y-y³
=8x³-y³
=(8x-y)(8x²+8xy+y²)
d) (3x-4)(x+4)+(5x-x)(2x²+3x-1)
=3x²+12x-4x-16+10x³+15x²-5x-2x³-3x²+x
=18x²+4x-16+5x³
e) 7x(x-4)-(7x+3)(2x²-x+4)
=7x²-28x-(14x³-7x²+28x+6x²-3x+12)
=7x²-28x-14x³+7x²-28x-6x²+3x-12
=8x²-14x³-53x-12