а ) 2 / 9 + 6 / 9 - 3 / 9 = ( 9 / 9 * 2 - 9 / 9 * 6 - 9 / 9 * 3 ) / 9 = (1 * 2 - 1 * 6 - 1 * 3) / 9 = (2 - 6 - 3) / 9 = ( - 4 - 3) / 9 = - 7 / 9;б )8 целых 25 / 27 - 3 целых 8 / 27 + 2 целых 3 / 27 = 8 + 25 / 27 - 3 - 8 / 27 + 2 + 3 / 27 = ( 8 - 3 + 2 ) + ( 25 / 27 - 8 / 27 + 3 / 27) = ( 5 + 2 ) + ( 25 / 27 - 8 / 27 + 3 / 27) = 7 + ( 25 / 27 - 8 / 27 + 3 / 27) = 7 + (25 - 8 + 3) / 27 = 7 + ( 25 - 5) / 27 = 7 целых 20 / 27;в ) (8 целых 3 / 17 - 7 целых 15 / 17 ) + 3 целых 16 / 17 = 8 + 3 / 17 - 7 - 15 / 17 + 3 + 16 / 17 = ( 8 - 7 + 3 ) + ( 3 / 17 - 15 / 17 + 16 / 17) = 4 + ( 3 - 15 + 16) / 17 = 4 целых 4 / 17.