Thanks Markiyan.

Actually, this method still left a couple of terms expressed in full (in terms of x,y rather than r1,r2), but of the two methods presented, I found this to give neater results when solving the entire expression.

Thank you so much. As I wrote above, I would vote you up but I don't have enough points yet. : (

Thanks Markiyan.

Actually, this method still left a couple of terms expressed in full (in terms of x,y rather than r1,r2), but of the two methods presented, I found this to give neater results when solving the entire expression.

Thank you so much. As I wrote above, I would vote you up but I don't have enough points yet. : (

Thanks Andri,

but I still get some terms expressed in full. I found that Markiyan's method (below) was able to give neater results for the whole expression (I only included a small part of the expression in my question).

Anyway, thanks again. I would vote you up but apparently I don't have enough points to do that. Sorry!

Thanks Andri,

but I still get some terms expressed in full. I found that Markiyan's method (below) was able to give neater results for the whole expression (I only included a small part of the expression in my question).

Anyway, thanks again. I would vote you up but apparently I don't have enough points to do that. Sorry!