Question

a) Tìm x biết : | 5x-4| = | x+2 |

b) Tìm x, y thuộc Z thỏa mãn x+xy+y =9

Answer 1

a)\(\left|5x-4\right|=\left|x+2\right|\)

\(\Rightarrow\left[{}\begin{matrix}5x+4=x+2\\5x+4=-x-2\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}5x+4-x-2=0\\5x+4+x+2=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}4x+2=0\\6x+6=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=-\dfrac{1}{2}\\x=-1\end{matrix}\right.\)

b) \(x+y+xy=9\)

\(\Rightarrow x+y+xy+1=10\)

\(\Rightarrow x\left(y+1\right)+1\left(y+1\right)=10\)

\(\Rightarrow\left(x+1\right)\left(y+1\right)=10\)