Question

7x (3x-1)+21 (3x-1)=0

Answer 1

Ta có: 7x(3x-1)+21(3x-1)=0

<=>7(3x-1)(x+3)=0

<=>3x-1=0 hoặc x+3=0

<=> x=\(\dfrac{1}{3}\) hoặc x=-3

Answer 2

Ta có:7x(3x-1)+21(3x-1)=0

=>(7x+21)(3x-1)=0

=>7(x+3)(3x-1)=0

\(\Rightarrow\left[{}\begin{matrix}7=0\left(loại\right)\\x+3=0\\3x-1=0\end{matrix}\right.\)

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

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

Vậy \(x\in\left\{-3;\dfrac{1}{3}\right\}\)