Question

What are $2$ perpendicular lines?

Answer 1

Two lines are said to be perpendicular if they intersect at right angles or the angle of inclination is $90°$. In the below figure, vertical and horizontal lines are two perpendicular lines.

Also, when two lines are perpendicular to each other, then the product of slopes of the lines will be $-1$. In other words, if the slope of a line is $m,$ then the slope of the line perpendicular to it will be $\frac{-1}{m}$.