A = |x - 9| + 2015
có |x - 9| > 0
=> |x - 9| + 2015 > 2015
=> Min A = 2015 <=> |x - 9| = 0
<=> x - 9 = 0
<=> x = 9
vậy Min A = 2015 khi x = 9
B = 5 - |x + 4|
có : |x + 4| > 0
=> - |x + 4| < 0
=> 5 - |x + 4| < 5
=> Max B = 5 <=> |x + 4| = 0
<=> x + 4 = 0
<=> x = -4
vậy_