a)Có: pt đt AB:\(\left\{{}\begin{matrix}vtcp\overrightarrow{AB}\left(-2;-6\right)\Rightarrow vtpt\overrightarrow{n}\left(6;-2\right)\\quaA\left(5;2\right)\end{matrix}\right.\)
=> \(AB:6x-2y-26=0\)
hay \(AB:3x-y-13=0\)
b) \(M\in Oy\Rightarrow M\left(0;y\right)\)
Có \(\overrightarrow{MA}\left(5;2-y\right),\overrightarrow{MB}\left(3;-4-y\right)\)
Do tam giác MAB cân tại M
\(\rightarrow MA=MB\Leftrightarrow MA^2=MB^2\Leftrightarrow5^2+\left(2-y\right)^2=3^2+\left(-4-y\right)^2\)
\(\Leftrightarrow y=\dfrac{1}{3}\)
Vậy \(M\left(0;\dfrac{1}{3}\right)\)