Question

X³.(x - 5)+3x.(x-5)=0

Answer 1

\(x^3\left(x-5\right)+3x\left(x-5\right)=0\)

\(x^4-5x^3+3x^2-15x=0\)

Chịu!!!!....

Answer 2

\(x^3\left(x-5\right)+3x\left(x-5\right)=0\Leftrightarrow\left(x^3+3x\right)\left(x-5\right)=0\Leftrightarrow x\left(x^2+3\right)\left(x-5\right)=0\)

\(\Leftrightarrow\hept{\begin{cases}x=0\\x^2+3=0\\x-5=0\end{cases}}\) ( vô lí vì \(x^2+3\ge3>0\) với mọi x)

Suy ra \(\hept{\begin{cases}x=0\\x=5\end{cases}}\)