Method for finding the potiential fuction f(x,y) given the gradient vector field F = < fx, fy>:
1) Evaluate f(x,y) = S fx dx = g(x,y) + C₁(y),
      where C₁(y) represents terms not containing x.
2) Evaluate f(x,y) = S fy dy = h(x,y) + C₂(x),
       where C₂(x) represents terms not containing y.
3) f(x,y) = g(x,y) + (sum of terms in h(x,y) not listed in g(x,y)) + K,
       where K is a constant

Proof of method: