Question

Giải các PT sau :

|2x-3x-5| = 5x + 5

| x^2 + 2x | = |x^2 - x - 2 |

| x^2 - 20x -9 | = | 3x^2 + 10x + 21 |

Answer 1

b: \(\Leftrightarrow\left[{}\begin{matrix}x^2-x-2=x^2+2x\\x^2-x-2=-x^2-2x\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}-3x-2=0\\2x^2+x-2=0\end{matrix}\right.\)

hay \(x\in\left\{-\dfrac{2}{3};\dfrac{-1+\sqrt{17}}{4};\dfrac{-1-\sqrt{17}}{4}\right\}\)

c: \(\Leftrightarrow\left[{}\begin{matrix}3x^2+10x+21=x^2-20x-9\\3x^2+10x+21=-x^2+20x+9\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}2x^2+30x+30=0\\4x^2-10x+12=0\end{matrix}\right.\Leftrightarrow x\in\left\{\dfrac{-15+\sqrt{165}}{2};\dfrac{-15-\sqrt{165}}{2}\right\}\)