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

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

x=-9+...+-9

x=-9.17

x=-153

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

8 nha bạn 

ht

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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

Đặt A=1.2.3+2.3.4+3.4.5+4.5.6+...+98.99.100

4A=(1.2.3+2.3.4+3.4.5+4.5.6+...+98.99.100)4

4A=1.2.3(4-0)+2.3.4(5-1)+3.4.5(6-2)+4.5.6(7-3)+...+98.99.100(101-97)

4A=1.2.3.4+2.3.4.5-1.2.3.4+3.4.5.6-2.3.4.5+4.5.6.7-3.4.5.6+...+98.99.100.101-97.98.99.100

4A=1.2.3.4-1.2.3.4+2.3.4.5-2.3.4.5+3.4.5.6-3.4.5.6+...+97.98.99.100-97.98.99.100+98.99.100.101

4A=98.99.100.101

=>A=98.99.100.101/4

=> A=24497550

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