a,71.2-6.(2x+5)=10^5:10^3
142-6.(2x+5)=10^2
142-6.(2x+5)=100
6.(2x+5)=142-100
6.(2x+5)=42
2x+5=42:6
2x+5=7
2x=7-5
2x=2
x=1
Vậy x=1
71.2-6.(2x+5)=105:103 d.125.(3x+2):13=1000:13
142-6.(2x+5)=100 125.(3x+2) = 1000/13.13
6.(2x+5)=142-100 125.(3x+2) =1000
6.(2x+5)=42 3x+2 =1000:125
2x+5 =42:6 3x+2 =8
2x+5 =7 3x=8-2=6
2x =7-5 tự làm phần còn lại
2x =2
x =2:2
x=1
(5x+34).68=69.34
(5x+34).68=29.313
(5x+34)=29.313:68
(5x+81)=2.35
5x=486-81
5x=405
x=81
12:(390:(5.100-(125+x.49)))=4
390:(5.100-(125+x.49))=12:4
390:(5.100-(125+x.49))=3
5.100-(125+x.49)=390:3
500-(125+x.49)=130
125+x.49=500-130
125+x.49=370
x.49=370-125
x.49=245
x=245:49
x=5