Ответ:

28/2=14; 14/2=7; 7/7=1, 28 = 2^2 * 742/2=21; 21/3=7; 7/7=1, 42 = 2*3*770/2=35; 35/5=7; 7/7=1, 70 = 2*5*714/2=7; 7/7=1, 14 = 2*7НОК (7;28;42;70;14) = 2^2 * 3 * 5 * 7 = 4203/7 * 60/60 = 180/420, 11/28 * 15/15 = 165/420, 1/2 * 210/210 = 210/420, 13/42 * 10/10 = 130/420, 23/70 * 6/6 = 138/4205/14 * 30/30 = 150 / 420. Ответ: 3/7, 11/28, 1/2