Giải thích các bước giải:
`a, qquad x(4x^3-5xy+2x)`
`=x.4x^3-x.5xy+x.2x`
`=4x^4-5x^2y+2x^2`
`b, qquad (x^2-xy+y^2)(2x+3y)`
`=2x(x^2-xy+y^2)+3y(x^2-xy+y^2)`
`=2x.x^2-2x.xy+2x.y^2+3y.x^2-3y.xy+3y.y^2`
`=2x^3-2x^2y+2xy^2+3x^2y-3xy^2+3y^3`
`=2x^3+3y^3-(2x^2y-3x^2y)+(2xy^2-3xy^2)`
`=2x^3+3y^3+x^2y-xy^2`
`c, qquad x^2(x+y)+2x(x^2+y)`
`=x^2 . x+x^2 . y+2x.x^2+2x.y`
`=x^3+x^2y+2x^3+2xy`
`=3x^3+x^2y+2xy`