Question

How are perpendicular lines similar to intersecting lines? How are they different ?

Answer 1

Perpendicular lines are a particular case of intersecting lines when an angle between them is `90^o`.

Explanation:

Any two lines on a plane that have exactly one common point are called intersecting.

Incidentally, other types of positions of two lines on a plane are parallel (no points of intersection) and coinciding (all points of one line are also points of another).

When two lines intersect, they form four angles, each having a vertex at the point of intersection.

If each of these four angles measures `90^o`, the intersecting lines are called perpendicular.
It is, actually, sufficient for perpendicularity to have only one of these four angles to measure `90^o` since other angles will automatically be `90^o` as well - proof is easy.