$X_1 = 100, Y_1 = 64$

$X_2 = 70, Y_2 = 34$

$X_3 = 50, Y_3 = 14$

I need to find the $Y = F(X)$ formula.

I can see that $X_2 - X_1 = Y_2 - Y_1$, but $X_2/X_1 \neq Y_2/Y_1$.

P.S. This is not homework, i'm trying to work out some CSS properties which affect each other, my math is just terrible. Thank you!

  • 3
    $\begingroup$ I believe $Y=X-36$ works. $\endgroup$ Commented Jul 2, 2020 at 17:25
  • $\begingroup$ Why I always complicate things and ignore simple operations :D ? $\endgroup$ Commented Jul 2, 2020 at 17:27
  • $\begingroup$ It's a good learning moment though! If changing $X$ always causes a proportional change in $Y$, then the equation you're looking for is linear, $Y=mX+b$. In this case, the "proportional" change in $Y$ is exactly the same change as the change in $X$, which is why $m=1$ in this case. $\endgroup$ Commented Jul 2, 2020 at 17:28
  • $\begingroup$ @GregMartin Thank you very much. This makes so much sense now! $\endgroup$ Commented Jul 2, 2020 at 17:31

1 Answer 1


There are many possibilities. Simple one is to : pass a circle through the 3 points and find its equation


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