По условию
AC/BC = m/n,
Но AC = AB+BC,
Тогда
(AB+BC)/BC = m/n,
(AB/BC) + 1 = m/n,
AB/BC = (m/n) - 1 = (m-n)/n
BC/AB = n/(m-n)
(BC/AB) + 1 = (n/(m-n)) + 1,
(BC+AB)/AB = (n+m-n)/(m-n) = m/(m-n),
BC + AB = AC,
AC/AB = m/(m-n).
Ответ. AC:AB = m:(m-n), BC:AB = n:(m-n).