Relative Position of Graphs of the Linear Functions

Suppose we are given two linear functions `y=k_1x+b_1` and `y=k_2x+b_2`.

Graphs of these functions are lines.parallel and intersecting lines

These lines intersect if `k_1!=k_2`. In particular, if `k_1k_2=-1` then lines are perpendicular.

These lines are parallel if `k_1=k_2`. In particular, if `b_1=b_2` then lines are same.

For example, lines `y=2x+3` and `y=2x-4` are parallel. Lines `y=4x+3` and `y=-0.25x+7` are perpendicular.