$(2x-1)^{4}$ = 625
⇒$(2x-1)^{4}$ = 5$x^{4}$
⇒ 2x-1 =±4
⇒\(\left[ \begin{array}{l}2x-1=4\\2x-1=-4\end{array} \right.\) ⇔ \(\left[ \begin{array}{l}2x=5\\2x=-3\end{array} \right.\) ⇔ \(\left[ \begin{array}{l}x=$\frac{5}{2}$ \\x=$\frac{-3}{2}$ \end{array} \right.\)
$(3x)^{2}$ = 81
⇒$(3x)^{2}$ = $9^{2}$
⇒ 3x=±9
⇒\(\left[ \begin{array}{l}3x=9\\3x=-9\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=9:3\\x=-9:3\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x=3\\x=-3\end{array} \right.\)
