A system of linear equations [tex] \left \{ {{a_1x+b_1y=c_1} \atop {a_2x+b_2y=c_2}} \right. [/tex] has:
1. unique solution, when: [tex] \frac{a_1}{a_2}\neq \frac{b_1}{b_2} [/tex];
2. no solutions, when: [tex] \frac{a_1}{a_2} = \frac{b_1}{b_2} \neq \frac{c_1}{c_2} [/tex];
3. infinitely many solutions, when: [tex] \frac{a_1}{a_2} = \frac{b_1}{b_2} = \frac{c_1}{c_2} [/tex].
According to the part 3 you can create such system:
[tex] \left \{ {{x-2y=3} \atop {_2x-4y=6}} \right. [/tex]
Graphs (the same line) are shown on the added picture.
