a)2x(8x-1)2 (4x-1)=9
\(\Leftrightarrow\text{ (64x}^2\text{-16x+1)(8x}^2\text{-2x)=9}\)
\(\Leftrightarrow\text{ 512x}^4\text{-256x}^3\text{+40x}^2\text{-2x=9}\)
\(\Leftrightarrow\text{ 512x}^4\text{-256x}^3\text{+40x}^2\text{-2x-9=0}\)
\(\Leftrightarrow\text{ 512x}^4\text{-128x}^3\text{-64x}^2\text{-128x}^3\text{+32x}^2\text{+16x+72x}^2\text{-18x-9=0}\)
\(\Leftrightarrow\text{ (512x}^4\text{-128x}^3\text{-64x}^2\text{)-(128x}^3\text{-32x}^2\text{-16x)+(72x}^2\text{-18x-9)=0}\)
\(\Leftrightarrow\text{ 64x}^2\text{(8x}^2\text{-2x-1)-16x(8x}^2\text{-2x-1)+9(8x}^2\text{-2x-1)=0}\)
\(\Leftrightarrow\text{ (64x}^2\text{-16x+9)(8x}^2\text{-2x-1)=0}\)
\(\Leftrightarrow\text{ (64x}^2\text{-16x+9)(8x}^2\text{-4x+2x-1)=0}\)
\(\Leftrightarrow\text{ (64x}^2\text{-16x+9)(2x-1)(4x+1)=0}\)
\(\Rightarrow\left\{{}\begin{matrix}2x-1=0\\4x+1=0\end{matrix}\right.\) (Vì 64x2 -16x+9 =0 )
\(\Rightarrow\left\{{}\begin{matrix}x=\frac{1}{2}\\x=-\frac{1}{4}\end{matrix}\right.\)
