\(a,x\left(x-3\right)=x^2-6\\ \Rightarrow x^2-3x-x^2=-6\\ \Rightarrow-3x=-6\\ \Rightarrow x=2\\ b,x^2-7x+12=0\\ \Rightarrow\left(x^2-3x\right)-\left(4x-12\right)=0\\ \Rightarrow x\left(x-3\right)-4\left(x-3\right)=0\\ \Rightarrow\left(x-3\right)\left(x-4\right)=0\\ \Rightarrow\left[{}\begin{matrix}x=3\\x=4\end{matrix}\right.\\ d,x^3-25x=0\\ \Rightarrow x\left(x^2-25\right)=0\\ \Rightarrow x\left(x-5\right)\left(x+5\right)=0\\ \Rightarrow\left[{}\begin{matrix}x0=\\x=5\\x=-5\end{matrix}\right.\)
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