Question

Tìm x biết rằng

a)x^3-4x^2+4x=0

b)x^3-9x=0

Answer 1

\(x^3-4x^2+4x=0\)
\(\Leftrightarrow x\left(x^2-4x+4\right)=0\)
\(\Leftrightarrow x\left(x-2\right)^2=0\)
\(\Leftrightarrow x=0\) hoặc \(x-2=0\)
\(\cdot x=0\)
\(\cdot x-2=0\Leftrightarrow x=2\)
Vậy \(S=\left\{0;2\right\}\)

\(x^3-9x=0\)
\(\Leftrightarrow x\left(x^2-9\right)=0\)
\(\Leftrightarrow x\left(x-3\right)\left(x+3\right)=0\)
\(\Leftrightarrow x=0\) hoặc \(x-3=0\) hoặc \(x+3=0\)
\(\cdot x=0\)
\(\cdot x-3=0\Leftrightarrow x=3\)
\(\cdot x+3=0\Leftrightarrow x=-3\)
Vậy \(S=\left\{0;\pm3\right\}\)