Выполните вычитание:а)6/7-9/14 б)9/20-5/12 в)5/9-3/8 г)7/18-1/45

а)

6/7 – 9/14 = (6 * 2 – 9) / 14 =  (12 – 9) / 14 = 3/14.

б)

9/20 – 5/12 = (9 * 3 – 5 * 5) / 60 = (27 – 25) / 60 = 2/60 = 1/30.

в)

5/9 – 3/8 = (5 * 8 – 3 * 9) / 72 = (40 – 27) / 72 = 13/72.

г)

7/18 – 1/45 = (7 * 5 – 1 * 2) / 90 = (35 – 2) / 90 = 33/90 = 11/30.