Bài 3:
a,(x-1)(x+2)=x2+2x-x-2=x2+x-2
b,(3+x)(x+1)=3x+3+x2+x=x2+4x+3
c,(x-1)(2x2-3x+1)
=2x3-3x2+x-2x2+3x-1
=2x3-5x2+4x-1
d,(2+x)(-x2+3x-1)
=-2x2+6x-2-x3+3x2-x
=-x3+x2+5x-2
e,(-0,4x-15x2)(-52x4-10x3+6)
=(0,4x+15x2)(52x4+10x3-6)
=x5+4x4-2,4x+12x6+2x5-65x2
=12x6+3x5+4x4-65x2-2,4x
f,(0,6x2+34x)(-253x3-20x3+4)
=-5x5-12x5+2,4x2-254x4-15x4+3x
=-17x5-854x4+2,4x2+3x
475
10989
292
làm mỗi a,b,c,d thôi đc ko c