1/ 1 + (-2) + 3 + (-4) + . . . + 17 + (-18)
= [1 + (-2)] + [3 + (-4)] + . . . + [17 + (-18)]
= (-1) + (-1) + . . . + (-1)
18 : 2 = 9
= (-1) . 9
= -9
2/ -1 + 2 - 3 + 4 + . . . - 99 + 100
= (-1 + 2) + (-3 + 4) + . . . (-99 + 100)
= 1 + 1 + . . . + 1
100 : 2 = 50
= 1 . 50
= 50
3/ 2 – 4 + 6 – 8 + . . . + 48 – 50 + 51 - 52
= (2 – 4) + (6 – 8) + . . . + (46 - 48) + (– 50 + 51 - 52)
= (-2) + (-2) + . . . + (-2) + (-51)
(48 - 2) : 2 + 1 = 24 : 2 = 12
= (-2) . 12 + (-51)
= (-24) + (-51)
= -75
4/ – 1 + 3 – 5 + 7 - . . . . + 97 – 99 + 101
= (–1 + 3) + (–5 + 7) + . . . . + (-93 + 95) + (97 – 99 + 101)
= 2 + 2 + . . . . + 2 + 99
(95 - 1) : 2 + 1 = 48 : 2 = 24
= 2 . 24 + 99
= 48 + 99
= 147
5/ 1 + 2 – 3 – 4 + . . . . + 97 + 98
= (1 + 2 – 3 – 4) + . . . . + (93 + 94 - 95 - 96) + (97 + 98)
= (-4) + . . . . + (-4) + 195
96 : 4 = 24
= (-4) . 24 + 195
= -96 + 195
= 99
1/ 1 + (-2) + 3 + (-4) + . . . + 17 + (-18)
=(1+3+5+..+17)+[-2+(-3)+(-4)+..+(-18)
goi ben tong so duong la A va tong so am la B ta co
A co ssh la :(17-1):2+1=9
B co ssh la :[-18-(-2)]:2+1=9
=>A=(17+1).9:2=81
=>B=[-18+(-2)].9:2=-72
=> A+B= 81+(-72)=9
vay tong bang 9