1,

a, $x^2-2xy+y^2-z^2=\left(x-y\right)^2-z^2$

=$\left(x-y-z\right)\left(x-y+z\right)$

b, hình như sai đề phải ko bn?

Phải là: $x^2-6x+9-9y^2$=$\left(x-3\right)^2-\left(3y\right)^2$$=\left(x-3y-3\right)(x+3y-3)$

c,$\left(x+y\right)\left(y+z\right)\left(x+z\right)+xyz$

=$(x^2+xy+yz+xz)\left(z+y\right)+xyz$

=$(x^2z+xyz+xz^2)+(x^2y+xy^2+xyz)+$$\left(yz^2+y^2z+xyz\right)$

= xz(x + y + z) + xy(x + y + z) + yz(x + y +z)

=(x+y+z)(xz+xy+yz)

2,a,$\left(x-2\right)\left(x+1\right)=0$$\Rightarrow$$\left[{}\begin{matrix}x-2=0\\x+1=0\end{matrix}\right.$

$\Rightarrow\left[{}\begin{matrix}x=2\\x=-1\end{matrix}\right.$

b,Đề phải thế này nha:

$5x\left(x-3\right)-x+3=0$$\Rightarrow$(x - 3)(5x - 1)=0

$\Rightarrow$$\left[{}\begin{matrix}x-3=0\\5x-1=0\end{matrix}\right.$$\Rightarrow$$\left[{}\begin{matrix}x=3\\x=\dfrac{1}{5}\end{matrix}\right.$

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