Đáp án:
a) ║2x+1║-20=-7
║2x+1║=-7+20
║2x+1║=13
2x+1=±13
TH1: 2x+1=13 TH2: 2x+1=-13
2x= 13-1 2x= -13-1
2x=12 2x= -14
x=12:2 x= -14: 2
x= 6 x= -7
b) -28-7.║-3x+15║=-70
-7.║-3x+15║=-28+70
-7.|-3x+15|= 42
|-3x+15|= 42:-7
|-3x+15|=-6
-3x+15=±6
TH1: -3x+15=6 TH2: -3x+15=-6
-3x=6-15 -3x=-6-15
-3x=-9 -3x= -21
x=-9:-3 x=-21:-3
x= 3 x=7
c) |18-2|.|-x+5|=12
|16|.|-x+5|=12
16.|-x+5|=12
|-x+5|=12:16
|-x+15|=3/4
x+15=±3/4
TH1: x+15=3/4 TH2: x+15=-3/4
x=3/4-15 x= -3/4-15
x=-57/4 x= -63/4
d) 12-2.(-x+3)²=-38
2.(-x+3)²=12+38
2.(-x+3)²=40
(-x+3)²=40:2
(-x+3)²=20
x+3=±20
TH1: x+3=20 TH2: x+3=-20
x=20-3 x=-20-3
x=17 x= -23
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