Question

Tìm X

a. 2.(x+3)-x²-3x=0

b. (2x+1)²-(x-1)²=0

c. x⁴-4x-3=0

Answer 1

a,

\(2\left(x+3\right)-x^2-3x=0\\ \Leftrightarrow2\left(x+3\right)-\left(x^2+3x\right)=0\\ \Leftrightarrow2\left(x+3\right)-x\left(x+3\right)=0\\ \Leftrightarrow\left(x+3\right)\left(2-x\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}x+3=0\\2-x=0\end{matrix}\right.\\ \Leftrightarrow\left[{}\begin{matrix}x=-3\\x=2\end{matrix}\right.\)

Vậy \(x\in\left\{-3;2\right\}\)

b,

\(\left(2x+1\right)^2-\left(x-1\right)^2=0\\ \Leftrightarrow\left(2x+1+x-1\right)\left(2x+1-x+1\right)=0\\ \Leftrightarrow3x\left(x+2\right)=0\\ \Leftrightarrow\left[{}\begin{matrix}3x=0\\x+2=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=-2\end{matrix}\right.\)

Vậy \(x\in\left\{0;-2\right\}\)