a) \(x^2-25-\left(x+5\right)=0\Leftrightarrow x^2-25-x-5=0\Leftrightarrow x^2-x-30=0\)
\(\Leftrightarrow x^2+5x-6x-30=0\Leftrightarrow x\left(x+5\right)-6\left(x+5\right)=0\)
\(\Leftrightarrow\left(x-6\right)\left(x+5\right)=0\Leftrightarrow\left\{{}\begin{matrix}x-6=0\\x+5=0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x=6\\x=-5\end{matrix}\right.\) vậy \(x=6;x=-5\)
b) \(\left(2x-1\right)^2-\left(4x^2-1\right)=0\Leftrightarrow4x^2-4x+1-4x^2+1=0\)
\(2-4x=0\Leftrightarrow4x=2\Leftrightarrow x=\dfrac{2}{4}=\dfrac{1}{2}\) vậy \(x=\dfrac{1}{2}\)
c) \(x^2\left(x^2+4\right)-x^2-4=0\Leftrightarrow x^2\left(x^2+4\right)-\left(x^2+4\right)=0\)
\(\Leftrightarrow\left(x^2-1\right)\left(x^2+4\right)=0\Leftrightarrow\left\{{}\begin{matrix}x^2-1=0\\x^2+4=0\end{matrix}\right.\) \(\Leftrightarrow\left\{{}\begin{matrix}x^2=1\\x^2=-4\left(vôlí\right)\end{matrix}\right.\)
ta có : \(x^2=1\Leftrightarrow x=\pm1\) vậy \(x=1;x=-1\)
