Drag the red and blue dots.
Finds the intercept of 2 lines. If the intercept disappeared, it is outside the screen. Red: Line 1 Blue: Line 2 Black: Intercept This uses Cramer’s rule which is too complicated for me to understand, so https://en.wikipedia.org/wiki/Line%E2%80%93line_intersection#Given_two_points_on_each_line
