bài 1
a)5ab(2a^2+3b -4)
=10a^3b+15ab^2-20ab
b)-3x(2x^2-4x+1/3)-(x-1)(x^2+x+1)
=-6x^3+12x^2-x-(x^3-1)
=-6x^3+12x^2-x-x^3+1
=5x^3+12x^2-x+1
c)(2x^3-5x^2-10x):2x+(x-2)(x+5)
=x^2-5/2x-5+x^2+5x-2x-10
=2x^2+1/2x-15
Bài 2
a)x^3-x^2y-4x+4y
=x^2(x-y)-4(x-y)
=(x-y)(x^2-4)
=(x-y)(x-2)(x+2)
b)x^2-16-4xy+4y^2
=(x^2-4xy+4y^2)-16
=(x-2y)^2-16
=(x-2y-4)(x-2y+4)
c)x(x-y)^2+y(y-x)^2
=x(x-y)^2+y(x-y)^2
=(x-y)^2(x+y)
Bài 3
a)(x+1)(x+2)-(x-3)(x+4)=7
x^2+2x+x+2-x^2-4x+3x+12=7
2x+14=7
x=-7/2
