.......
8х - 7х-1=2(4х+3)
8х-7х-1=8х+6
8х-8х-7х=6+1
- 7х=7
х= - 1
7(2х+1) - 6(3х+1)=2*6*7
14х+7-18х-6=84
- 4х=84-7+6
-4х=83
х= - 20,75
2(2х+3)-5х-13+3(5-2х)=6*6
4х+6-5х-13+15-6х=36
-7х=28
х= - 4
4х²+5х+2(10-2х²)=5*14
4х²+5х+20-4х²=70
5х=70-20
5х=50
х=10