The derivative of a quotient u/vu/vu/v is:
(u′v−uv′)/v2(u'v - uv') / v^2(u′v−uv′)/v2
(u′v+uv′)/v2(u'v + uv') / v^2(u′v+uv′)/v2
u′/v′u' / v'u′/v′
u′v/v2u'v / v^2u′v/v2