Bài 6:
a) \(=x\left(x-3\right)+y\left(x-3\right)=\left(x-3\right)\left(x+y\right)\)
b) \(=x^3\left(x-9\right)+x\left(x-9\right)=x\left(x-9\right)\left(x^2+1\right)\)
c) \(=x^2\left(x-4\right)-9\left(x-4\right)=\left(x-4\right)\left(x^2-9\right)\)
\(=\left(x-4\right)\left(x-3\right)\left(x+3\right)\)
d) \(=x^2\left(x+1\right)+x\left(x+1\right)+\left(x+1\right)=\left(x+1\right)\left(x^2+x+1\right)\)
e) \(=x^2\left(x^2-2\right)+2x\left(x^2-2\right)+2\left(x^2-2\right)\)
\(=\left(x^2-2\right)\left(x^2+2x+2\right)\)
f) \(=x^2\left(x-3\right)-x\left(x-3\right)+9\left(x-3\right)=\left(x-3\right)\left(x^2-x+9\right)\)
Bài 7:
a) \(\Rightarrow x^2\left(x+5\right)-9\left(x+5\right)=0\)
\(\Rightarrow\left(x+5\right)\left(x-3\right)\left(x+3\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=-5\\x=3\\x=-3\end{matrix}\right.\)
b) \(\Rightarrow9\left(5-x\right)+\left(5-x\right)^2=0\)
\(\Rightarrow\left(5-x\right)\left(14-x\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}x=5\\x=14\end{matrix}\right.\)
