Bonjour,

1)

- 175/- 25 = (25 x 7) / (25 x 1) = 7

- 38/114 = (38 x - 1) / (38 x 3) = - 1/3

1,21/- 7,7 = (1,21 x 100) / (7,7 x 100) = 121/770 = (11 x 11) / (11 x 70) = 11/70.

2)

a + b = 12/7 - 4/7 = 8/7

a - b = 12/7 - (- 4/7) = 12/7 + 4/7 = 16/7

a + b = - 5/2 + 1/4 = (- 5 x 2) / (2 x 2) + 1/4 = - 10/4 + 1/4 = - 9/4

a - b = - 10/4 - 1/4 = - 11/4

a + b = - 2/3 + (- 3/4) = (- 2 x 4) / (3 x 4) - (3 x 3) / (4 x 3) = - 8/12 - 9/12 = - 17/12

a - b = - 2/3 - (- 3/4) = - 2/3 + 3/4 = - 8/12 + 9/12 = 1/12.