1) \(\Leftrightarrow3\sqrt{5x}-4\sqrt{5x}+8\sqrt{5x}=21\)
\(\Leftrightarrow7\sqrt{5x}=21\)
\(\Leftrightarrow\sqrt{5x}=3\)
\(\Leftrightarrow5x=9\)
\(\Leftrightarrow x=\frac{9}{5}\)
2)\(\Leftrightarrow x^2-10x+25=16\)
\(\Leftrightarrow x^2-10x+9=0\)
\(\Leftrightarrow\left(x-9\right)\left(x-1\right)=0\)
\(\Leftrightarrow\orbr{\begin{cases}x-9=0\\x-1=0\end{cases}}\Leftrightarrow\orbr{\begin{cases}x=9\\x=1\end{cases}}\)