Đáp án:
`A = 2xyz.(-5x^2 y^3)`
`= [2.(-5)] . (x.x^2).(y.y^3).z`
`= -10x^3 y^4 z`
`B = (-3/4x^5 y^4).(xy^2).(-8/9x^2 y^5)`
`= [(-3/4).(-8/9)].(x^5 .x.x^2).(y^4 .y^2.y^5)`
`= 2/3 x^8 y^11`
`C = (x^3.9-5/4x^2 y).(2/5x^3 y^4)^3`
`= (9x^3 - 5/4 x^2 y).[(2/5)^3 .(x^3)^3 . (y^4)^3]`
`= (9x^3 - 5/4 x^2 y). (8/125 . x^9 . y^12)`
`= 9x^3 . 8/125 .x^9 .y^12 + (-5/4 x^2 y). 8/125 . x^9 . y^12`
`= (9. 8/125).(x^3 . x^9).y^12 + (-5/4 . 8/125).(x^2 . x^9) .(y . y^12)`
`= 72/125 x^12 y^12 - 2/25 x^11 y^13`
