(-25)-(5.x-3)=4
5.x-3 = -25 - 4
5.x-3=-29
5.x=-26
x=-26/5
x=-5,2
5.x-6=20-(12-6)
5.x-6=20-6
5.x-6=14
5.x=20
x=20:5
x=4
vậy x=4
1/
-25-(5x-3)=4
-25-4=5x-3
-25-4+3=5x
5x= -26
x= -26/5
2/
5x-6=20-(12-6)
5x = 20-12+6+6
5x = 20
x = 20/5 = 4
3/
-2x -40 = (5-x) -(-15+60
-2x -40 = 5-x +15-60
-2x +x = 5+15-60+40
-x = 0
x=0