Specific Parabolic Equation with Two Known Points and a known point of diminishing returns

24 Views Asked by At

I am looking for a specific parabola that is horizontal opening toward -x (So a backward C). All of the values in this scenario concern Quadrant 1, and have these rules:

  1. y-values are whole numbers.
  2. Point 1 is (185, 1), and is slightly -x,+y from the vertex
  3. Point 2 is (85, 40), Further -x,+y from the vertex, this is the point of diminishing returns going negative.
  4. If you multiply the coordinate pair values, the total should get higher as x decreases, and y increases from 1 to 40 (up and to the left), but any multiplication of y=41 and higher should begin to lower.

So:

  • (y=1) * (x=185) = 185
  • (y=2) * x > 185
  • (y=3) * x > 2x
  • 4x > 3x
  • ...
  • (y=40) * (x=85) = 3400
  • (y=41) * x < 3400
  • (y=42) * x < 41x
  • ...

I found this equation which is close: x = 185 - y^2/16, but it caps at the coordinate where y=32 : (121, 32) and begins to lower from there, so I'm not quite there.

I may need to solve this again for two different points, so knowing a tool or process to solve it would be wonderful. But my requirement right now is this specific scenario.