a
\(x^2=25\\ \Leftrightarrow\left[{}\begin{matrix}x=5\\x=-5\end{matrix}\right.\)
b
\(\left(x+2\right)^2=81\\ \Leftrightarrow\left[{}\begin{matrix}x+2=9\\x+2=-9\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=7\\x=-11\end{matrix}\right.\)
c
\(16-\left(x+2\right)^2=7\\ \Leftrightarrow\left(x+2\right)^2=9\\ \Leftrightarrow\left[{}\begin{matrix}x+2=3\\x+2=-3\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=1\\x=-5\end{matrix}\right.\)
d
\(2x^2+1=7\\ \Leftrightarrow x^2=\dfrac{7-1}{2}=3\\ \Leftrightarrow x=\pm\sqrt{3}\)
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