`a)20x-5y`
`=5.4x-5.y`
`=5(4x-y)`
`b)20x²y+12x³`
`=4x².5y+4x².3x`
`=4x²(5y+3x)`
`c)8x^4y+12x²y²+20x³y^4`
`=4x²y.2x²+4x²y.3y+4x²y.5xy³`
`=4x²y(2x²+3y+5xy³)`
`d)3x(x+1)+5y(x+1)`
`=(x+1)(3x+5y)`
`e)3x(x-6)-2(6-x)`
`=3x(x-6)-2(-x+6)`
`=3x(x-6)+2(x-6)`
`=(x-6)(3x+2)`
`f)4y(x-1)-(1-x)`
`=4y(x-1)-(-x+1)`
`=4y(x-1)+(x-1)`
`=(x-1)(4y+1)`
`g)4x²-1=(2x)²-1²=(2x+1)(2x-1)`
`h)125x³+1=(5x)³+1³=(5x+1)(25x²-5x+1)`
`i)x^4+2x²+1=(x^2)^2+2.x².1+1²=(x²+1)²`
`k)` Sửa đề:`4x²-12xy+y²`
`→4x²-12xy+9y²`
`4x²-12xy+9y²=(2x)²-2.2x.3y+(3y)²=(2x-3y)²`
