Question

Tìm x, biết:

x³ - 3x² - x + 3

Giúp mình với, ngày mai cô kiểm tra bài rồi.

Answer 1

Chắc là \(x^3-3x^2-x+3=0\)

\(\Leftrightarrow\left(x^3-x\right)-\left(3x^2-3\right)=0\)

\(\Leftrightarrow x\left(x^2-1\right)-3\left(x^2-1\right)=0\)

\(\Leftrightarrow\left(x-3\right)\left(x^2-1\right)=0\)

\(\Leftrightarrow\left(x-3\right)\left(x-1\right)\left(x+1\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=3\\x=1\\x=-1\end{matrix}\right.\)

Answer 2

\(x^3-3x^2-x+3=0\)

\(\Leftrightarrow x^2\left(x-3\right)-\left(x-3\right)=0\)

\(\Leftrightarrow\left(x-3\right)\left(x+1\right)\left(x-1\right)=0\)

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