\(a,3x\left(x+1\right)+9\left(x+1\right)\\ =\left(3x+9\right)\left(x+1\right)\\ =3\left(x+3\right)\left(x+1\right)\\ b,x^2-5xy+2x-10y\\ =x\left(x-5y\right)+2\left(x-5y\right)\\ =\left(x+2\right)\left(x-5y\right)\)
BÀI 2: Phân tích thành nhân tử .
`a, 3x(x+1)+9(x+1)`
`= (x+1)(3x+9)`
`=3(x+1)(x+3)`
`b,x^2-5xy+2x-10y`
`=x(x-5y)+2(x-5y)`
`=(x-5y)(x+2)`