u/(u-v) - 4uv/(u2-v2) - v/(v-u)
= u/(u-v) - 4uv/(u2-v2) + v/(u-v)
= u(u+v)/((u-v)(u+v)) - 4uv/(u2-v2) + v(u+v)/((u-v) (u+v))
= (u(u+v) - 4uv+ v(u+v))/((u-v) (u+v))
= (u2 + uv - 4uv+ uv +v2))/((u-v) (u+v))
= (u2 - 2uv +v2))/((u-v) (u+v))
= (u-v)2/((u-v) (u+v))
= (u-v)/(u+v)
(ohne Gewähr. Bitte nachrechnen)