Question

Tìm x :

b) x⁵ - 18x³ + 81x = 0

Answer 1

\(x^5-18x^3+81x=0\)

\(\Leftrightarrow\left(x^5-9x^3\right)-\left(9x^3-81x\right)=0\)

\(\Leftrightarrow x^3\left(x^2-9\right)-9x\left(x^2-9\right)=0\)

\(\Leftrightarrow\left(x^3-9x\right)\left(x^2-9\right)=0\)

\(\Leftrightarrow x.\left(x^2-9\right)\left(x^2-9\right)=0\)

\(\Leftrightarrow x.\left(x^2-9\right)=0\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x^2-9=0\end{array}\right.\)

\(\Leftrightarrow\left[\begin{array}{nghiempt}x=0\\x^2=9\end{array}\right.\Rightarrow\left[\begin{array}{nghiempt}x=0\\x=\pm3\end{array}\right.\)

Vây ..................