Đáp án:
`12) 10x(x-y)-8y(y-x)`
`= 10x(x-y)+8y(x-y)`
`=(10x-8y)(x-y)`
`=2(5x-4y)(x-y)`
`13) 2/5 x(y-1)- 2/5 y (y-1)`
`= (2/5 x - 2/5 y)(y-1)`
`= 2/5 ( x-y)(y-1)`
`14) 2/5 x² + 5x³ + x²y`
`= x²( 2/5 + 5x + y)`
`15) 14x²y - 21xy² + 28x²y²`
`= 7xy(2x - 3y + 4xy)`
`16) 5y¹⁰ - 15y⁸`
`= 5y⁸(y² - 3)`
`17)3x(x-1) + 7x² ( x-1)`
`= x(3+7x)(x-1)`
`18) 6y² (x-1) + 9y(x-1)²`
`= [6y²+9y(x-1)](x-1)`
`=(6y²+9xy-9y)(x-1)`
`= 3y(2y + 3x -3)(x-1)`
`19) 4x(x-2y) + 8y ( 2x-y)`
`= 4(x-2y)²`
`20) a² ( x-1)+b²(1-x)`
`=(a-b)(a+b)(x-1)`
`21) x(m-a)-y(m-a)-z(m-a)`
`=(x-y-z)(m-a)`
