Factorization

[Johnny Leong]

r^2 - xyr + (r^2)s + (x)r^2 - (y)r^2 + rsy

Which terms should be grouped together for factorization? Please give some comments.

[Pyrrhus]

First they all have r, start from there, the group those with similar variables.

[Johnny Leong]

I found that this question cannot be factorized as a very simple answer. If really do factorization, only group several terms together, factorize something out but then cannot proceed.