Đáp án+Giải thích các bước giải:
`a) 3x(5x^2-2x-1)`
`=3x.5x^2-3x.2x-3x.1`
`= 15x^3-6x^2-3x`
`b) (x^2+2xy-3)(-xy)`
`=x^2.(-xy)+2xy.(-xy)-3.(-xy)`
`=-x^3y-2x^2y^2+3xy`
`c) 1/2x^2y(2x^3-2/5xy^2-1)`
`=1/2x^2y.2x^3-2/5xy^2 . 1/2x^2y-1 . 1/2x^2y`
`=x^5y-1/5x^3y^3- 1/2x^2y`
`d) {4x-2(x-3)-3[x-3(4-2x)+8]}.(-3x)`
`=[4x-2x+6-3(x-12+6x+8)].(-3x)`
`=(4x-2x+6-3x+36-18x-24).(-3x)`
`=[(4x-2x-3x-18x)+(6+36-24)].(-3x)`
`= (-19x+18).(-3x)`
`=(-19x).(-3x)+18.(-3x)`
`=57x^2-54x`
