Đáp án:
$\begin{array}{l}
a)y = ax + b\,đi\,qua\,O\,và A\\
\Rightarrow \left\{ \begin{array}{l}
0 = 0 + b\\
1 = a.2 + b
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
b = 0\\
a = \frac{1}{2}
\end{array} \right. \Rightarrow y = \frac{1}{2}x\\
b)y = a'x + b'\,đi\,qua\,O\,và\,B\\
\Rightarrow \left\{ \begin{array}{l}
b' = 0\\
- 2 = a' + b'
\end{array} \right. \Rightarrow \left\{ \begin{array}{l}
b' = 0\\
a' = - 2
\end{array} \right. \Rightarrow y = - 2x\\
c)\,ta\,thấy:a.a' = \frac{1}{2}.\left( { - 2} \right) = - 1\\
\Rightarrow hai\,đường\,thẳng\,vuông\,góc
\end{array}$