17

-2 x -3/(-5) = -2x3/5 = -6/5

-2/3 x (-5) = 2x5/3 = 10/3

7 x (-3/5) = -3x7/5 = -21/5

18

- 7/4 x 2/3 = -7x2/4x3 = -14/12 = -7/6

-6/5 x (-25/12) = 6x25/5x12= 150/60

 150/60 simplifié :   6x5x5/5x6x2 = 5/2

-3/2 x 1/9 = -3x1/2x9 = -3/18 = -1/6

17/8,1 x 8,1/7 = 17/7

12/7 x 14/15 = 12x14/7x15 = 168/105

 168/105 simplifié : 3x4x7x2/7x3x5 = 8/5

-4/3 x 9/8 = -4x9/3x8 = -36/24 = -6/4 = -3/2