1)[( m² + mn - 4mn)/ (m + n )] : [(mn - m² - n² - mn + 2mn)/(n2 - m²)] = [(m ² - 3mn)/(m + n )] : [(- m² - n² + 2mn)/(n² - m2)] = [m(m - 3n9/(m + n)] * [(m - n)(m + n)/(m - n )²] = m(m - 3n)/( m - n)
если m = 1/5, а n = - 4/5, то 1/5 * (1/5 + 12/5)/ (1/5 + 4/5) = 13/25 = 0, 52