a.\(\left(x-1\right)^2+x\left(4-x\right)=11\)
\(\Leftrightarrow x^2-2x+1+4x-x^2=11\)
\(\Leftrightarrow2x=10\)
\(\Leftrightarrow x=5\)
b. \(x^2-9-2\left(x+3\right)=0\)
\(\Leftrightarrow x^2-9-2x-6=0\)
\(\Leftrightarrow x^2-2x-15=0\)
\(\Leftrightarrow\left\{{}\begin{matrix}x=5\\x=-3\end{matrix}\right.\)