2) \(\left(x+3\right)\left(5x-15\right)+2x-6=0\)
\(\Leftrightarrow\left(x+3\right).5.\left(x-3\right)+2\left(x-3\right)=0\)
\(\Leftrightarrow\left(x-3\right)\left[5\left(x+3\right)+2\right]=0\)
\(\Leftrightarrow\left(x-3\right)\left(5x+17\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-3=0\\5x+17=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=3\\x=-\dfrac{17}{5}\end{matrix}\right.\)
câu 1 phải là \(\left(x-5\right)\left(x+9\right)+6x=30\)
\(\Leftrightarrow\left(x-5\right)\left(x+9\right)+6x-30=0\)
\(\Leftrightarrow\left(x-5\right)\left(x+9\right)+6\left(x-5\right)=0\)
\(\Leftrightarrow\left(x-5\right)\left(x+9+6\right)=0\)
\(\Leftrightarrow\left(x-5\right)\left(x+15\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x-5=0\\x+15=0\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=-15\end{matrix}\right.\)
