Объяснение:

№7

1) 9/14 - (-5/21) = 9/14 + 5/21 = 27/42 + 10/42 = 37/42

2) 37/42 : (-2 9/14) = 37/42 : (-37/14) = 37/42 * (-14/37) = 1/3 * (-1/1) = -1/3

№8

1) 7/16 - 31/40 = 35/80 - 62/80 = 27/80

2) -17/24 + 27/40 = -85/120 + 81/120 = -4/120 = -1/30

3) 27/80 : (-1/30) = 27/80 * (-30/1) = 27/8 * (-3/1) = -81/8 = -10 1/8

№9

1) -4,5 : 9/14 = -45/10 * 14/9 = -5/5 * 7/1 = -35/5 = -7

2) -8 2/9 - (-7) = -8 2/9 + 7 = -1 2/9

3) -1 2/9 * 2 1/4 = -11/9 * 9/4 = -11/4 = -2 3/4

4) -3 3/4 - (-2 3/4) = -3 3/4 + 2 3/4 = -1