x2 + 5x + 6
= x2 + 2x + 3x + 6
= x(x + 2) + 3(x + 2)
= (x + 2)(x + 3)
7x - 6x2 - 2
= - 6x2 + 7x - 2
= - 6x2 + 3x + 4x - 2
= - 3x(2x - 1) + 2(2x - 1)
= (2x - 1)(-3x + 2)
mk ko pit lm câu a, xl nhé
\(\text{a) }xy\left(x+y\right)+yz\left(y+z\right)+xz\left(x+z\right)+2xyz\\ \\=x^2y+xy^2+y^2z+yz^2+x^2z+xz^2+xyz+xyz\\ \\=\left(x^2y+xy^2+x^2z+xyz\right)+\left(xz^2+yz^2+y^2z+xyz\right)\\ \\=x\left(xy+y^2+xz+yz\right)+z\left(xz+yz+y^2+xy\right)\\ \\=\left(x+z\right)\left(xy+y^2+xz+yz\right)\\ =\left(x+z\right)\left[\left(xy+y^2\right)+\left(xz+yz\right)\right]\\=\left(x+z\right)\left[y\left(x+y\right)+z\left(x+y\right)\right]\\ \\=\left(x+z\right)\left(y+z\right)\left(x=y\right) \)
\(\text{b) }x^2+5x+6\\ \\ =x^2+2x+3x+6\\ \\=\left(x^2+2x\right)+\left(3x+6\right)\\ \\=x\left(x+2\right)+3\left(x+2\right)\\ \\=\left(x+2\right)\left(x+3\right)\)
\(\text{c) }7x-6x^2-2\\ \\ =3x+4x-6x^2-2\\ \\ =\left(3x-6x^2\right)-\left(2-4x\right)\\ \\ =3x\left(1-2x\right)+2\left(1-2x\right)\\ \\ =\left(3x+2\right)\left(1-2x\right)\)
