`#040911`
`a)`
`(2x - 1)^2 - (2x + 5)(2x + 1) = 10`
`\Leftrightarrow 4x^2 - 4x + 1 - (4x^2 + 12x + 5) = 10`
`\Leftrightarrow 4x^2 - 4x + 1 - 4x^2 - 12x - 5 = 10`
`\Leftrightarrow (4x^2 - 4x^2) - (4x + 12x) + (1 - 5) = 10`
`\Leftrightarrow -16x - 4 = 10`
`\Leftrightarrow -16x = 10 + 4`
`\Leftrightarrow -16x = 14`
`\Leftrightarrow x = \dfrac{-7}{8}`
Vậy, `x= \dfrac{-7}{8}`
`b)`
`9^2(x - 1) + 25(1 - x) = 0`
`\Leftrightarrow 9^2(x - 1) - 25(x - 1) = 0`
`\Leftrightarrow (x - 1)(9^2 - 25) = 0`
`\Leftrightarrow`\(\left[{}\begin{matrix}x-1=0\\9^2-5^2=0\end{matrix}\right.\)
`\Leftrightarrow`\(\left[{}\begin{matrix}x=1\\\left(9-5\right)\left(9+5\right)=0\end{matrix}\right.\)
\(\Leftrightarrow\left[{}\begin{matrix}x=1\\4\cdot14=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=1\\56=0\left(\text{vô lý}\right)\end{matrix}\right.\\ \text{Vậy, x = 1}\)
`c)`
\(x^2+3x-4=0\)
`\Leftrightarrow x^2 + 4x - x - 4 = 0`
`\Leftrightarrow (x^2 - x) + (4x - 4) = 0`
`\Leftrightarrow x(x - 1) + 4(x - 1) = 0`
`\Leftrightarrow (x + 4)(x - 1) = 0`
\(\Leftrightarrow\left[{}\begin{matrix}x+4=0\\x-1=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-4\\x=1\end{matrix}\right.\\ \text{ Vậy, }x\in\left(-4;1\right)\)
