Question

Tìm x

x³ -\(\dfrac{9}{49}\)x = 0

Answer 1

\(x^3-\dfrac{9}{49}x=0\\ \Rightarrow x^3=\dfrac{9}{49}x\\ \Rightarrow x^2\cdot x=\left(\pm\dfrac{3}{7}\right)^2\cdot x\\ \Rightarrow x^2=\left(\pm\dfrac{3}{7}\right)^2\\ \Rightarrow x=\left[{}\begin{matrix}\dfrac{3}{7}\\-\dfrac{3}{7}\end{matrix}\right.\)

Answer 2

Bạn kia bị thiếu mất 1 nghiệm , mình làm lại :

\(x^3-\dfrac{9}{49}x=0\)

\(\Leftrightarrow x\left(x^2-\dfrac{9}{49}\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0\\x^2=\dfrac{9}{49}\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=0\\x=\pm\dfrac{3}{7}\end{matrix}\right.\)

KL.....