a/ \(7x\left(x+1\right)-3\left(x+1\right)=0\)
\(\Leftrightarrow\left(x+1\right)\left(7x-3\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-1\\x=\frac{3}{7}\end{matrix}\right.\)
b/ \(3\left(x+8\right)-x^2-8x=0\)
\(\Leftrightarrow3\left(x+8\right)-x\left(x+8\right)=0\)
\(\Leftrightarrow\left(x+8\right)\left(3-x\right)=0\)
\(\Leftrightarrow\left[{}\begin{matrix}x=-8\\x=3\end{matrix}\right.\)
c/ \(x^2-10x=-25\)
\(\Leftrightarrow x^2-10x+25=0\)
\(\Leftrightarrow\left(x-5\right)^2=0\)
\(\Leftrightarrow x-5=0\)
\(\Leftrightarrow x=5\)
