`(x-2)^2 -4x+8=0`

`<=> (x-2)^2 -(4x-8)=0`

`<=> (x-2)^2 - 4(x-2)=0`

`<=> (x-2)(x-2-4)=0`

`<=>(x-2)(x-6)=0`

\(\Leftrightarrow\left[{}\begin{matrix}x-2=0\\x-4=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=2\\x=4\end{matrix}\right.\)

\(c,\dfrac{\sqrt{x}-1}{\sqrt{x}+2}+\dfrac{5\sqrt{x}-2}{x-4}\\ =\dfrac{\left(\sqrt{x}-1\right)\left(\sqrt{x}-2\right)}{x-4}+\dfrac{5\sqrt{x}-2}{x-4}\\ =\dfrac{x-2\sqrt{x}-\sqrt{x}+2}{x-4}+\dfrac{5\sqrt{x}-2}{x-4}\\ =\dfrac{x-2\sqrt{x}-\sqrt{x}+2+5\sqrt{x}-2}{x-4}\\ =\dfrac{x+2\sqrt{x}}{x-4}\\ =\dfrac{\sqrt{x}\left(\sqrt{x}+2\right)}{x-4}\\ =\dfrac{\sqrt{x}}{\sqrt{x}-2}\)

\(b,\dfrac{\sqrt{x}}{\sqrt{x}-3}+\dfrac{2\sqrt{x}-2}{x-9}\\ =\dfrac{\sqrt{x}}{\sqrt{x}-3}+\dfrac{2\sqrt{x}-2}{x-9}\\ =\dfrac{\sqrt{x}\left(\sqrt{x}+3\right)}{x-9}+\dfrac{2\sqrt{x}-2}{x-9}\\ =\dfrac{x+3\sqrt{x}+2\sqrt{x}-2}{x-9}\\ =\dfrac{x-5\sqrt{x}-2}{x-9}\)

\(a,\dfrac{3}{\sqrt{x}-5}+\dfrac{20-2\sqrt{x}}{x-25}\\ =\dfrac{3}{\sqrt{x}-5}+\dfrac{20-2\sqrt{x}}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\\ =\dfrac{3\left(\sqrt{x}+5\right)}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}+\dfrac{20-2\sqrt{x}}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\\ =\dfrac{3\sqrt{x}+15+20-2\sqrt{x}}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\\ =\dfrac{\sqrt{x}+35}{\left(\sqrt{x}-5\right)\left(\sqrt{x}+5\right)}\)

\(-7+x=-3\\ \Rightarrow x--3-\left(-7\right)\\ \Rightarrow x=-3+7\\ \Rightarrow x=4\\ -456-x=723\\ \Rightarrow x=-456-723\\ \Rightarrow x=-1179\\ -124-312+x=-415\\ \Rightarrow312+x=-124+415\\ \Rightarrow312+x=291\\ \Rightarrow x=291-312\\ \Rightarrow x=-21\\ -214+512-\left(-163\right)-x=-768-\left(-423\right)\\ \Rightarrow-214+512+163-x=-345\\ \Rightarrow512+163-x=-345+214\\ \Rightarrow512+163-x=-131\\ \Rightarrow163-x=-131-512\\ \Rightarrow163-x=-643\\ \Rightarrow x=163+643\\ \Rightarrow x=806\)