A^2-9b^2/3ab :(1/3b -1/a) A=8 4/7 B= 4 1/7

Упростим смешанные дроби:

А = 8 4/7 = (8 * 7 + 4)/7 = 60/7;

В = 4 1/7 = (4 * 7 + 1)/7 = 29/7;

Получим пример ((60/7)^2 - 9 * (29/7)^2)/(3 * 60/7 * 29/7) : (1/3 * 29/7 - 1/(60/7)), который решим по действиям:

1) (60/7)^2 - 9 * (29/7)^2 = 3600/49 - 7569/49 = -3969/49 = -81;

2) 3 * 60/7 * 29/7 = (3 * 60 * 29)/(7 * 7) = 5220/49;

3) 1/3 * 29/7 -1/(60/7) = 29/21 - 7/60 = 29 * 20/420 - 7 * 7/420 = (580 - 49)/420 = 531/420;

4) -81/(5220/49) : 531/420 = -81 * 49/5220 * 420/531 = -(81 * 49 * 420)/(5220 * 531) = -1029/1711.