Find what percent of a line a point makes up

Question

I have two points, x2 and x1. I have their corresponding y's, y2 and y1.

I always know that x2>.95>x1 and that y2>y1.

so i wrote this code, in the hopes that I can basically find where along y1-y2 that .95 occurs, however I am not sure towards its accurancy, so any suggestions or notices would be nice:

  3 x1 = float(raw_input('x1: '))
  4 x2 = float(raw_input('x2: '))
  5 y1 = float(raw_input('y1: '))
  6 y2 = float(raw_input('y2: '))
  7 
  8 z = 0.95
  9 
 10 dist = x2-x1
 11 
 12 yi = ((1-(.01*(dist/(dist-(x2-z)))))*(y2-y1))+y1

please let me know if this is right, because I am not sure it is, but I am also not sure what I am missing.

Answer 1

The equation of a line is y = mx + c where m is the slope, and c is the intercept.

Given (x1, y1) and (x2, y2) , you can find m and c :

m = (y2-y1)/(x2-x1)
c = y2 - m * x2

Now that you know those, you can find the value of y when x = 0.95 , by:

y = m * 0.95 + c

Answer 2

The equation of a line by two points (x1, y1) and (x2, y2) is (y-y1)/(y2-y1) = (x-x1)/(x2-x1) . if xi = 0.95 , then yi = (y2-y1)*(xi-x1)/(x2-x1)+y1