I have tried to submit this question [
In general, given two expressions, $\sqrt{A+B\sqrt{N}}$ and $\sqrt{C+D\sqrt{N}}$, under what conditions is it possible to add or subtract the two so a to yield a third expression, $\sqrt{E+F\sqrt{N}}$. [A, B, C, D, E, F and N are integers, with N not a perfect square]?
] to M.SE. It responds with a message to the effect that the question could not be submitted because of the error stated above (or words to that effect). The problem is that no error has been stated. What gives?