1.
Any 3 lines a, b and c intersect and form triangles, in no 2 of them are parallel.
2.
2 lines are parallel only if their slopes are equal.
3.
if the equation of a line l is given in the form y=mx+t, then m, the coefficient of x, is the slope of that line.
4.
so given lines a, b, c with equations:
[tex]a: y=m_1x+t\\\\b: y=m_2x+u\\\\c: y=m_3x+v[/tex]
if [tex]m_1 \neq m_2 \neq m_3[/tex], then the lines intersect, forming thus a triangle.
5.
let the 3 lines be:
[tex]a: y=2x+5\\\\b: y=-4x+13\\\\c: y=x+7[/tex]
