Question

Tìm x biết :  a) \(\left|x^3-x-1\right|=x^3+x+1\) 

b) \(\left|x^4+x^2+1\right|=x^2-x-1\) 

Answer 1

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

câu b) tương tự

 

Answer 2

b) Ta có: \(\left|x^4+x^2+1\right|=x^2+x+1\)

\(\Leftrightarrow x^4+x^2+1=x^2+x+1\)

\(\Leftrightarrow x^4-x=0\)

\(\Leftrightarrow x\left(x-1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x=1\end{matrix}\right.\)