line | through (f_x, f_y) through (v_x, v_y) (assuming focus (f_x, f_y) and vertex (v_x, v_y))

(drawn with rotation angle 0°)

y = (x (f_y - v_y))/(f_x - v_x) + (-f_y v_x + f_x v_y)/(f_x - v_x)

y - f_y = ((x - f_x) (f_y - v_y))/(f_x - v_x)

y (f_x - v_x) + f_y v_x - f_x v_y + x (v_y - f_y) = 0 (assuming focus (f_x, f_y) and vertex (v_x, v_y))

x-intercept | (f_y v_x - f_x v_y)/(f_y - v_y) y-intercept | (f_x v_y - f_y v_x)/(f_x - v_x) slope | (f_y - v_y)/(f_x - v_x) (assuming focus (f_x, f_y) and vertex (v_x, v_y))

from (f_x, f_y) to (v_x, v_y): sqrt((f_x - v_x)^2 + (f_y - v_y)^2)

between (f_x, f_y) and (v_x, v_y): (1/2 (f_x + v_x), 1/2 (f_y + v_y)) = (0.5 (f_x + v_x), 0.5 (f_y + v_y))