Bài toán 3 :
a) 5 – (12 – x) = 129 – (6 + 129)
<=> 5 - 12 + x = 129 - 6 - 129
<=> x = 129 - 6 - 129 - 5 + 12
<=> x = 1
b) 20 – (x + 3) = - 45 – (17 – 45)
<=> 20 - x - 3 = -45 - 17 + 45
<=> -x = -45 - 17 + 45 + 3 - 20
<=> -x = -34
<=> x = 34
c) 24 + (17 – x) = (125 – 30) – 125
<=> 24 + 17 - x = 95 - 125
<=> -x = 95 - 125 - 17 - 24
<=> -x = -71
<=> x = 71
d) 3(x – 4) – (8 – x) = 12
<=> 3x - 12 - 8 + x = 12
<=> 3x + x = 12 + 8 + 12
<=> 4x = 32
<=> x = 8
e) x – (13 – x) = - 24 + (-7 + x)
<=> x - 13 + x = -24 - 7 + x
<=> x + x - x = -24 -7 + 13
<=> x = -18
f) (x – 7) + (5 – x) = 12 – (-8 + x)
<=> x - 7 + 5 - x = 12 + 8 - x
<=> x - x + x = 12 + 8 + 7 - 5
<=> x = 22
g) 124 + (13 – 16) = 162 – (x + 162)
<=> 124 + 13 - 16 = 162 - x - 162
<=> x = 162 - 162 - 124 - 13 + 16
<=> x = -121
h) 5(x – 6) – 2(x + 3) = 12
<=> 5x - 30 - 2x - 6 = 12
<=> 5x - 2x = 12 + 6 + 30
<=> 3x = 48
<=> x = 16
