Firstly thanks for the quick reply despite it being in the wrong section, very new at this whole thing.

does

satisfy the condition because it's in the same form as the original set?

I've multiplied out the

to get a_1(x+y\sqrt{-5}) + b_1(x\sqrt{-5} - 5y) but I'm not sure if this satisfies the condition, or whether I've written it in the write form. Could you possibly explain why it does satisfy the conditions?

Thanks again. (Nod)