28 = 42 - 2x
42 - 2x = 28
2x = 42 - 28
2x = 14
x = 14 : 2
x = 7
-18+42=42-2x
=> 24 = 42 - 2x
=> 2x = 42 - 24
=> 2x = 18
=> x = 18 : 2
=> x = 9
Vậy x = 9
\(-18+42=42-2x\)
\(24=42-2x\)
\(2x=42-24\)
\(2x=18\)
\(x=9\)
42 -2x =-18+42
-2x = -18+42-42
-2x = -18
2x=18
x=18 :2
x=9
duyệt đi chúc bn học giỏi