The given equations are : ax + by – c = 0 and lx + my – n = 0
Here, a1 = a, b1 = b, c1 = –c, and a2 = l, b2 = m, c2 = – n
For unique solution,
\(\frac{a_1}{a_2}\) \(\ne\) \(\frac{b_1}{b_2}\), i.e, \(\frac{a}{l}\)\(\ne\) \(\frac{b}{m}\) \(\Rightarrow\) am \(\ne\) bl