Bạn tham khảo:
a) $-7 < x ≤ 5$
$⇒ x ∈$ { $-6; -5; -4; -3; -2; -1; 0; 1; 2; 3; 4 ;5$ }
Tổng $= -6 + ( -5 + 5 ) + ( -4 + 4 ) + ( -3 + 3 ) + ( -2 + 2 ) + ( -1 + 1 ) + 0 = -6$
b) $-3≤ x < 8$
$⇒ x ∈$ { $-3; -2; -1; 0; 1; 2;3;4;5;6;7$ }
Tổng $= ( -3 + 3 ) + ( -2 + 2 ) + ( -1 + 1 ) + 0 + 4 + 5 + 6 + 7 = 22$
c) $| x | < 7$
$⇒ x ∈ ${ $-6; -5; -4; ... ; 4; 5;6$ }
Tổng $= ( -6 + 6 ) + ( -5 + 5 ) + ( -4 + 4 ) + ... + ( -1 + 1 ) + 0 = 0 $
