a) \(({d_1}) \equiv ({d_2})\) khi và chỉ khi \(\left\{ \matrix{m + 1 = 2 \hfill \cr n = 5 \hfill \cr} \right. \Leftrightarrow \left\{ \matrix{m = 1 \hfill \cr n = 5 \hfill \cr} \right..\)
b) \((d_1)\) cắt \((d_2)\) \(⇔ m + 1 \neq 2 ⇔ m \ne 1.\)
c) \(({d_1})\parallel ({d_2}) \Leftrightarrow \left\{ \matrix{m + 1 = 2 \hfill \cr n \ne 5 \hfill \cr} \right. \Leftrightarrow \left\{ \matrix{m = 1 \hfill \cr n \ne 5 \hfill \cr} \right.\)
