b) 1-3+5-7+9-11+......+2005-2007

=(1-3)+(5-7)+(9-11)+.....+(2005-2007)

=(-2)+(-2)+(-2)+......+(-2)

=(-2).1004

=(-2008)

c) 1+2+3-4-5-6+7+8+9-10-11-12+...+97+98+99-100-101-102

=(1+2+3-4-5-6)+(7+8+9-10-11-12)+.....+(97+98+99-100-101-102)

=(-9)+(-9)+....+(-9)

=(-9).17

=(-153)

Xin lỗi nha 2 dòng cuối mk làm sai 

b)1-3+5-7+9-11+......+2005-2007

=(1-3)+(5-7)+(9-11)+....+(2005-2007)

=(-2)+(-2)+(-2)+....+(-2)

=(-2).502

=(-1004)

1+2+3-4-5-6+...+97+98+99-100-101-102

=(1+2+3-4-5-6)+...+(97+98+99-100-101-102)  có 17 cặp số

=(-9)+(-9)....+(-9) 17 cặp số

=(-9).17=-153

ủa tính nhanh hay tính giá trị biểu thức hay tính thường dợ bên đó

1+2-3-4+5+6-7-8+9+10-11-12+13+98-99-100+101+102 = 103

1+2-3-4+5+6-7-8+9+10-11-12+13+98-99-100+101+102

= 1 + (2-3-4+5)+(6-7-8+9)+(10-11-12+13)+(98-99-100+101)+102

= 1 + 0 + 0 + 0 + 0 +102

= 103

????????????????????

x=(1+2+3-4-5-6)+...+(97+98+99-100-101-102)

x=-9+...+-9

x=-9.17

x=-153

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D = 1+2+3-4-5-6+7+8+9-10-11-12+........+97+98+99-100-101-102

D = (1+2+3-4-5-6) + (7+8+9-10-11-12) + ........... + (97+98+99-100-101-102)

D = (-9) + (-9) + .......... + (-9) có 17 số -6

D = -6.(-9)

D = 54

cau nay chinh con me no

con nay la 1209876

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(1+2+3-4-5-6)+(7+8+9-10-11-12)+....+(97+98+99-100-101-102)=-27+-27+...+-27

                                                                                          =-27*17=-153

neu dug thi tk nha