Question

Tìm x:

a)2x(x+5)+(x+5)=0

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

c) 2x(x-2)-(x-2)\(^2\)=0

 

Answer 1

`2x(x+5)+(x+5)=0`

`<=>(x+5)(2x+1)=0`

\(\Leftrightarrow\left[{}\begin{matrix}x+5=0\\2x+1=0\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=0-5\\2x=-1\end{matrix}\right.\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-5\\x=\dfrac{-1}{2}\end{matrix}\right.\)

`-------------`

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

`x.` đúng hơn bn?

`-----------`

`2x(x-2)-(x-2)^2=0`

`<=> (x-2) (2x-x+2)=0`

`<=>(x-2)(x+2)=0`

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

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

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