Докажите, что если a/b = c/d, то: 1) (a - b)/b = (c - d)/d; 2) a/(a + b) = c/(c +d).

1) (a - b)/b = (c - d)/d; (a - b) * d = (c - d) * b;ad - bd = cb - db;ad = cb; a/b = c/d - верно2) a/(a + b) = c/(c +d);a/(c +d) = c/(a + b)ac + ad = cа + cbаd = bсa/b = c/d - верно