Je ne m'en sort pas

exercice 2
1) 1-2×=0
-2×=-1
×=1/2

2) 6×+2-2 (×-5)=×+7
6×+2-2×+10=×-7
6×-2×-×=7-2-10
3×=-5
×=-5/3

3) (2×+3)/4=3
2×+3=3×4
2×=12-3
×=9/2

4) [(×+1)/3]-[(×-1)/5]=1
[(5×+5)/15]-[(3×-3)/15]=1
[5×+5-(3×-3)]/15
5×+5-3×+3=15
2×+8=15
2×=7
×=7/2