Lớp 8 không làm thế.
\(\left(2x-1\right)^2-\left(2x+1\right)^2=4\left(x-3\right)\)
\(\Leftrightarrow\left[\left(2x-1\right)+\left(2x+1\right)\right]\left[\left(2x-1\right)-\left(2x+1\right)\right]=4\left(x-3\right)\)
\(\Leftrightarrow\left(4x\right)\left(-2\right)=4\left(x-3\right)\)
\(2x=-x+3\Rightarrow x=3\)
Đáp số: x=3
\(\left(2x-1\right)^2-\left(2x+1\right)^2=4\left(x-3\right)\)
\(\Leftrightarrow\left(2x^2-2x.1+1^2\right)-\left(2x^2+2x.1+1^2\right)=4x-12\)
\(\Leftrightarrow2x^2-2x+1-2x^2+2x-1-4x=-12\)
\(\Rightarrow-4x=-12\Rightarrow x=3\)
Vậy.....................................
