u^3 - 3uv^2 = 259
3u^2v - v^3 = -286
u( u^2 - 3v^2) = 259 (1)
v(3u^2 - v^2) = -286 (2)
Note that a possible factorization of 259 is 7 * 37
Letting u = 7
Then
7 ( 3*7^2 - v^2) = 259 which implies that
u^2 - 3v^2 = 37
7^2 - 3v^2 = 37
49 - 3v^2 = 37
12 = 3v^2
4 = v^2
v = 2 or v = -2
So if u = 7 and v = 2
Then
2 ( 3*7^2 - 2^2) > 0 so v = 2 isn't valid for (2)
If u = 7 and v = -2 then
-2 ( 3*7^2 - (-2)^2 ) = -2 ( 147 - 4) = - 2 ( 143) = -286
So
u = 7 v = -2
u^2 + v^2 = 7^2 + (-2)^2 = 49 + 4 = 53