Réponse :
1) -3/7 x -7/3 = 21/21 = 1
2) 12/-25 x -25/12 = 300/300 = 1
3) 4/-27 x -27/4 = 108/108 = 1
4) -4.5 x 1/-4.5 = 4.5/4.5 = 1
5) 2.8/4 x 4/2.8 = 11.2/11.2 = 1
6) 77/-33 x -33/77 = 2541/2541 = 1