d) Ta có: \(3x\left(x-7\right)-x+7\)
\(=3x\left(x-7\right)-\left(x-7\right)\)
\(=\left(x-7\right)\left(3x-1\right)\)
e) Ta có: \(3x^2-21x-2x+14\)
\(=3x\left(x-7\right)-2\left(x-7\right)\)
\(=\left(x-7\right)\left(3x-2\right)\)
f) Ta có: \(x^2+2xy-4z^2+y^2\)
\(=\left(x^2+2xy+y^2\right)-4z^2\)
\(=\left(x+y\right)^2-\left(2z\right)^2\)
\(=\left(x+y-2z\right)\left(x+y+2z\right)\)
g) Ta có: \(x^2-y^2+5x-5y\)
\(=\left(x-y\right)\left(x+y\right)+5\left(x-y\right)\)
\(=\left(x-y\right)\left(x+y+5\right)\)
h) Sửa đề: \(x^2-y^2+6y-9\)
Ta có: \(x^2-y^2+6y-9\)
\(=x^2-\left(y^2-6y+9\right)\)
\(=x^2-\left(y-3\right)^2\)
\(=\left(x-y+3\right)\left(x+y-3\right)\)
d) Ta có: 3x(x−7)−x+73x(x−7)−x+7
=3x(x−7)−(x−7)=3x(x−7)−(x−7)
=(x−7)(3x−1)=(x−7)(3x−1)
e) Ta có: 3x2−21x−2x+14
=3x(x−7)−2(x−7)=3x(x−7)−2(x−7)
=(x−7)(3x−2)=(x−7)(3x−2)
f) Ta có: x2+2xy−4z2+y2
=(x2+2xy+y2)−4z2
=(x+y)2−(2z)2
=(x+y−2z)(x+y+2z)
g) Ta có: x2−y2+5x−5y
=(x−y)(x+y)+5(x−y)
=(x−y)(x+y+5)
h)Ta có: x2_y2+6y−9
=x2_(y2_6y+9)
=x2−(y−3)2
=(x−y+3)(x+y−3)
