Question

giải các phương trình: (2x+5)(x-4)+3(x-4)=0

Answer 1

\(\left(2x+5\right)\left(x-4\right)+3\left(x-4\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(\left(2x+5\right)+3\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(2x+5+3\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left(2x+8\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\2x+8=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=4\\2x=-8\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-\dfrac{8}{2}\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)

Answer 2

\(\left(2x+5\right)\left(x-4\right)+3\left(x-4\right)=0\)

\(\Leftrightarrow\left(x-4\right)\left[\left(2x+5\right)+3\right]=0\)

\(\Leftrightarrow\left(x-4\right)\left(2x+8\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x-4=0\\2x+8=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=4\\x=-4\end{matrix}\right.\)