exercice n 2 de mathematique

2+9/15
=30/15+9/15
=39/15
1/2+3/4-5/8
=4/8+6/8-5/8
=10/8-5/8
=5/8
4/12+4/6-5/2+3/2
=4/12+8/12-8/2
=12/12-4
=1-4
=-3