who is line,

Do you mean Line as a geometry concept, or LINE the messaging app, or something else?

If you mean geometry:

• A line is an undefined term in Euclidean geometry: a straight one-dimensional figure that extends without endpoints in both directions (infinite length, zero thickness).
• Through any two distinct points, there is exactly one line.
• In the plane, lines can intersect at a point or be parallel (never intersect in the plane).
• Common ways to describe a line in 2D:
  • Slope-intercept form: y = mx + b (m is slope, b is y-intercept)
  • Point-slope form: y − y1 = m(x − x1) using a known point (x1, y1) on the line
  • Standard form: Ax + By = C
• Line vs line segment vs ray:
  • Line: extends forever in both directions
  • Line segment: endpoints and finite length
  • Ray: starts at a point and extends infinitely in one direction
• Quick example: The line through (2,3) and (5,9) has slope m = (9−3)/(5−2) = 2, so y − 3 = 2(x − 2) ⇒ y = 2x − 1.

If you meant LINE the app or something else, tell me and I’ll tailor the summary.