Trả lời:
a, 9 - ( 12 - x ) = 11
<=> 9 - 12 + x = 11
<=> -3 + x = 11
<=> x = 11 + 3
<=> x = 14
Vậy x = 14
b, -2x - ( -17 ) = 15
<=> -2x + 17 = 15
<=> -2x = 15 - 17
<=> -2x = -2
<=> x = -2 : (-2)
<=> x = 1
Vậy x = 1
mik nghĩ a = 14
\(a,9-\left(12-x\right)=11\Leftrightarrow x=14\)
\(b,-2x-\left(-17\right)=15\Leftrightarrow x=1\)