\(\left(x+1\right)\left(x+4\right)\left(x+2\right)\left(x+3\right)-3=0\)
\(\Leftrightarrow\left(x^2+5x+4\right)\left(x^2+5x+6\right)-3=0\)
Đặt \(x^2+5x+4=t\)
\(t\left(t+2\right)-3=0\Leftrightarrow t^2+2t-3=0\Rightarrow\left[{}\begin{matrix}t=1\\t=-3\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}x^2+5x+4=1\\x^2+5x+4=-3\end{matrix}\right.\) \(\Rightarrow\left[{}\begin{matrix}x^2+5x+3=0\\x^2+5x+7=0\end{matrix}\right.\) (bấm máy)
\(\left(8x-1\right)^22x\left(4x-1\right)-9=0\)
\(\Leftrightarrow\left(64x^2-16x+1\right)\left(8x^2-2x\right)-9=0\)
Đặt \(8x^2-2x=t\Rightarrow64x^2-16x=8t\)
\(\left(8t+1\right)t-9=0\)
\(\Leftrightarrow8t^2+t-9=0\Rightarrow\left[{}\begin{matrix}t=1\\t=-\frac{9}{8}\end{matrix}\right.\)
\(\Rightarrow\left[{}\begin{matrix}8x^2-2x=1\\8x^2-2x=-\frac{9}{8}\end{matrix}\right.\) \(\Leftrightarrow\left[{}\begin{matrix}8x^2-2x-1=0\\64x^2-16x+9=0\end{matrix}\right.\) (bấm máy)
