Bài 1:
a, 2*x - 12 -x = 0
x * ( 2-1) -12 = 0
x* 1 = 0 +12
x= 12
b, 2*x + 69 * 2 = 69 *4
2 * ( 69 + x) = 69 * 2 * 2
2 * (69 + x) = 138 * 2
=> 69 + x = 138
x = 138 - 69 = 69
Bài 2:
A=112-114+116-118+120-122+124
= ( 112 + 116) + (120 + 124) - ( 114 + 118 + 122)
= 228 + 244 - 354
= 118