(2\7-3\4)*(2\13-1\2) с пояснением

(2/7 - 3/4) * (2/13 - 1/2) = 9/56
1) 2/7 - 3/4 = 8/28 - 21/28 = - 13/28
2) 2/13 - 1/2 = 4/26 - 13/26 = - 9/26
3) - 13/28 * (- 9/26) = - 1/28 * (- 9/2) = 9/56