a, \(A\left(-1;-20\right);B\left(3;8\right)\inđths\Leftrightarrow\left\{{}\begin{matrix}-a+b=-20\\3a+b=8\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=7\\b=-13\end{matrix}\right.\)
b, \(M\left(4;-3\right)\inđths;\left(d\right)//đths\Leftrightarrow\left\{{}\begin{matrix}a=-\dfrac{2}{3}\\b\ne1\\4a+b=-3\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=-\dfrac{2}{3}\\b=-\dfrac{1}{2}\end{matrix}\right.\)
d, PTHDGD 2 đt đề cho là \(-\dfrac{1}{2}x+1=3x+5\Leftrightarrow\dfrac{7}{2}x=-4\Leftrightarrow x=-\dfrac{8}{7}\Leftrightarrow y=\dfrac{11}{7}\Leftrightarrow A\left(-\dfrac{8}{7};\dfrac{11}{7}\right)\)
\(A\left(-\dfrac{8}{7};\dfrac{11}{7}\right)\inđths;y=\dfrac{1}{2}x//đths\Leftrightarrow\left\{{}\begin{matrix}-\dfrac{8}{7}a+b=\dfrac{11}{7}\\a=\dfrac{1}{2};b\ne0\end{matrix}\right.\Leftrightarrow\left\{{}\begin{matrix}a=\dfrac{1}{2}\\b=\dfrac{15}{7}\end{matrix}\right.\)
