## Featured Replies in this Discussion

- by Gribouillis
- by Gribouillis

You have to solve the equation first.

after some equivalent transformations:

y*d=a*b-e-x*c

If d==0 and c==0 then x,y can be anything if a*b-e==0 else nothing

if d==0 and c!=0 then y= anything, x=(a*b-e)/c

if d!=0 and c==0 then y=(a*b-e)/d, x is anything

if d!=0 and c!=0 then x,y can be an infinite number of pairs so that if x is given, then y= (a*b-e-x*c)/d

After that the program is pretty trivial.

When one of c or d is not zero, the equation has an infinite number of solutions. In fact the solutions of `x * c + y * d = f`

are

```
x = (f * c - z * d)/(c**2 + d**2)
y = (f * d + z * c)/(c**2 + d**2)
```

Here z can be any real number.

When c = d = 0, the equation has no solution if f is not zero, otherwise every pair (x, y) is a solution.

Thank you both for the suggestions. Let me define this a bit: I'm trying to calculate liquids. There is no chance of either **c** or **d** being 0.

From what you've suggested, it looks like there'd be infinite solutions. If what I'm looking for in the final solution is the smallest y possible, how should I tackle this?

Sidenote: please do share links to pages that will help me understand that sort of equations better if you happen to have them / know how to find them. My math is a mess, as I've already said, and when I'm searching for similar equations I just get confused by what I find.

The solution

```
x = (f * c)/(c**2 + d**2)
y = (f * d)/(c**2 + d**2)
```

is minimum for the norm sqrt(x**2 + y**2). The set of solutions is a straight line in the plane (x, y) and this solution is the orthogonal projection of (0,0) on the line of solutions.

If you want to minimize y, there are 2 cases: if c == 0, then y is constant = f/d, if c != 0, the minimum for y is -infinity. If you want the minimal y >= 0, then you must chose x = f/c, y = 0.