\(5x\left(x-2\right)-5x^2=30\)
\(\Leftrightarrow5x^2-10-5x^2=30\)
\(\Leftrightarrow-10x=30\)
\(\Leftrightarrow x=-3\)
Dòng 2 là 10x nhé, ghi nhầm
\(5x\cdot\left(x-2\right)-5x^2=30\)
\(5x\cdot\left(x-2-x\right)=30\)
\(5x\cdot\left(-2\right)=30\)
\(5x=-15\)
\(x=-3\)