Bạn tham khảo :
$A = 11 -12 +13 -14+ 15 -16+ 17 -18 +19 -20+ ... +99 -100$
$A = (11 -12) +(13 -14)+ (15 -16)+( 17 -18) +(19 -20)+ ... +(99 -100)$
$A = (-1) + (-1) + ... + (-1)$
$A = (-1).50$
$A = (-50)$
$B = 101 - 102 -(-103 ) - 104 -(-105) - 106 -(-107) - 108 - (-109) -110$
$B = 101 - 102 + 103 - 104 + 105 - 106 + 107 - 108 + 109 - 110$
$B = (101 - 102 )+ (103 - 104 )+ (105 - 106 )+ (107 - 108 )+ (109 - 110)$
$B = (-1) + (-1)+ (-1)+(-1)+(-1)$
$B = (-1).5$
$B = (-5)$