x√18 - √18 = x√8 + 4√2
3x√2 - 3√2 = 2x√2 + 4√2
3x√2 - 2x√2 = 4√2 + 3√2
x√2 = 7√2
x = 7
\(x\sqrt{18}-\sqrt{18}=x\sqrt{8}+4\sqrt{2}\\\Leftrightarrow x\sqrt{18}-\sqrt{18}=2\sqrt{2}x+4\sqrt{2}\\ \Leftrightarrow\sqrt{18}\left(x-1\right)=2\sqrt{2}\left(x+2\right)\\ \Leftrightarrow3\sqrt{2}\left(x-1\right)=2\sqrt{2}\left(x+2\right)\\ \Leftrightarrow3x-3=2x+4\\ \Leftrightarrow x=7\)
Vậy x = 7