\(\left(\alpha\right):2x-y-1=0\Rightarrow\overrightarrow{n_1}=\left(2;-1;0\right)\)
\(\left(\alpha\right)//\left(\beta\right)\Rightarrow\overrightarrow{n_1}.CP.\overrightarrow{n_2}\Rightarrow\overrightarrow{n_2}=\left(2;-1;0\right)\)
\(\Rightarrow\left(\beta\right):2\left(x-1\right)-\left(y-0\right)=0\)
\(\Rightarrow\left(\beta\right):2x-y-2=0\)
mà \(\left(\beta\right):-x+by+cz+d=0\) hay \(2x-2by-2cz-2d=0\)
\(\Rightarrow\left\{{}\begin{matrix}-2b=-1\\-2c=0\\-2d=-2\end{matrix}\right.\)
\(\Rightarrow\left\{{}\begin{matrix}b=\dfrac{1}{2}\\c=0\\d=1\end{matrix}\right.\)
\(\Rightarrow S=b+c-3d=\dfrac{1}{2}+0-3.1=-\dfrac{5}{2}\)
