Đáp án:
bài 1:
`a) 2x(x^2-7x-3)=2x^3-14x^2-6x`
`b) (-2x^3+3/4y^2-7xy).4xy^2=-8x^2y^2+3xy^4-28x^2y^3`
`c) (25x^2+10xy+4y^2).(5x-2y)`
`=125x^3-8y^3`
`d) (2x+1)(3x+4)=6x^2+8x+3x+4=6x^2+11x+4`
bài 2:
`a) 4x-8y=4(x-2y)`
`b) x^2+2xy+y^2=(x+y)^2`
`c) 2xy+3zy+6y+xz=(2xy+xz)+(3zy+6y)`
`=x(2y+z)+3y(z+2y)`
`=(2y+z)(x+3y)`
`d) 3x^3-6x^2+3x=3x(x^2-2x+1)=3x(x-1)^2`
`e) 3x^2+5x-3xy-5y=x(3x+5)-y(3x+5)=(3x+5)(x-y)`
`f) x^3-10x^2+25x=x(x^2-10x+25)=x(x-5)^2`
`g) xy+y^2-x-y=y(x+y)-(x+y)=(x+y)(y-1)`
`h) x^3-4x^2-xy^2+4x=x(x^2-4x+4-y^2)`
`=x[(x-2)^2-y^2]=x(x-y-2)(x+y-2)`
`i) x^2-10x+25=(x-5)^2`
`k) x^2-64=(x-8)(x+8)`
`l) x^2+6x+9-y^2=(x+3)^2-y^2=(x-y+3)(x+y+3)`