https://ggplot2.tidyverse.org/reference/geom_abline.html
Reference lines: horizontal, vertical, and diagonal — geom_abline • ggplot2
These geoms add reference lines (sometimes called rules) to a plot, either horizontal, vertical, or diagonal (specified by slope and intercept). These are...
reference lineshorizontalverticaldiagonalgeom
https://www.mathopenref.com/coordperpendicular.html
Perpendicular lines. (Coordinate Geometry) - Math Open Reference
How to determine if lines are perpendicular in coordinate geometry
math open referenceperpendicular linescoordinate geometry