Bonjour
1)
15 x 2 = 30 et 6 x 5 = 30
2)
- 8/15 + 5/6 = (- 8 x 2) / (15 x 2) + (5 x 5) / (6 x 5)
3)
- 8/15 + 5/6 = - 16/30 + 25/30 = 9/30
4)
9/30 = (3 x 3) / (3 x 10) = 3/10.