4/7a+3/4a-5/8a при a=2 11/26

4/7a+3/4a-5/8a  = a (4/7+3/4-5/8) = a * (32+42-35)/56 = a *39/56 = {a= 2 11/26 = 63/26} =  63/26 *39/56 = 27/16 = 1 11/16