a)
`2x(x^2+xy+3)`
`=2x.x^2+2x.xy+2x.3`
`=2x^3+2x^2y+6x`
b)
`(5x-3)(2x+y+10)`
`=5x(2x+y+10)-3(2x+y+10)`
`=5x.2x+5x.y+5x.10-3.2x-3.y-3.10`
`=10x^2+5xy+15x-6x-3y-30`
`=10x^2+5xy+9x-3y-30`
c)
`x^3y^4:x^3y`
`=(x^3:x^3).(y^4:y)`
`=y^3`
d)
`(15x^3y^2+7xy-6xy):3xy`
`=(15x^3y^2+1xy):3xy`
`=15x^3y^2:3xy+1xy:3xy`
`=5x^2y+1/3`
e)
`(x^3-3x^2+x-3):(x-3)`
`=[(x^3-3x^2)+(x-3)]:(x-3)`
`=[x^2(x-3)+(x-3)]:(x-3)`
`=[(x-3)(x^2+1)]:(x-3)`
`=x^2+1`
PTĐTTNT:
`x^3+2x^2y+y^2x+2y^3`
`=(x^3+2x^2y)+(xy^2+2y^3)`
`=x^2(x+2y)+y^2(x+2y)`
`=(x+2y)(x^2+y^2)`
