Bài 1: Tìm Tổng
b)1-3+5-7+9-11+......+2005-2007
c) 1+2+3-4-5-6+7+8+9-10-11-12+...+97+98+99-100-101-102
Giúp với ạ. Mình cảm ơn
Tính tổng : a) S2 = 1 - 3 + 5 - 7 + 9 - 11 + ... + 2005 - 2007. b) S3 = 1 + 2 + 3 - 4 - 5 - 6 + 7 + 8 + 9 - 10 - 11 - 12 + ... + 97 + 98 + 99 - 100 - 101 - 102
1. [ ( -2 ). 3 + 9 ]. ( -5 ) - ( -6 ). 8
2. ( 135 - 35 ). ( -47 ) + 53. ( -48 - 52 )
3. 0 - 1 + 2 - 3 + 4 - 5 + 6 - 7 + ... + 2004 - 2005
4. 1 - 3 + 5 - 7 + 9 - 11 + ... + 2005 - 2007
5.1 + 2 + 3 - 4 - 5 - 6 + 7 + 8 + 9 - 10 - 11 - 12 + ... + 97 + 98 + 99 - 100 - 101 - 102
1.Tính tổng
A=0-1+2-3+4-5+6-7+.........+2017-2018
B=1-3+5-7+9-11+....+2005-2007
C=1+2+3-4-5-6+7+8+9-10-11-12+.....+97+98+99-100-101-102
A = 0-1 + 2-3 + 4-5 +...+ 2017-2018
=> A = (-1) + (-1) + (-1) +...+ (-1) (Có 1009 số hạng)
=> A = 1009.(-1)
=> A = -1009
B = 1-3+5-7+ 9-11+....+2005-2007
=> B = (-2) + (-2) +(-2) +...+ (-2) (Có 502 số hạng)
=> B = 502.(-2)
=> B = -1004
C=1+2+3-4-5-6+7+8+9-10-11-12+.....+97+98+99-100-101-102
=> C = (1+2+3-4-5-6)+...+(97+98+99-100-101-102) (có 17 cặp số)
=> C = (-9) + (-9) +...+ (-9) (có 17 số hạng)
=> C = (-9).17
=> C = -153
số 2 : tính nhanh
A = 99 - 97 + 95 -93 + 91 - 89 + .......... + 7 - 5 + 3 - 1
B = 50 - 49 + 48 - 47 + 46 - 45 + ........... + 4 - 3 + 2 - 1
C = 100 + 98 + 96 + ......... + 2 - 97 - 95 - ......... - 1
D = 1 + 3 + 5 + 7 + ......... + 999
E = 1 + 11 + 21 + 31 + ......... + 991
F = 3 + 7 + 11 + 15 + ......... + 99
H = 1 + 2 + 3 - 4 - 5 - 6 + 7 + 8 + 9 - 10 - 11 - 12 + .......... + 97 + 98 + 99 - 100 -101 - 102
I = 1 - 3 + 5 5 - 7 + 9 - 11 + ... + 2004 - 2007
K = -1 + 2 - 3 + 4 - 5 + 6 - 7 +.... + 2004 - 2005
G =1 - 2 - 3 + 4 + 5 - 6 - 7 + 8 +..... + 2004 + 2005
N = 1 - 4 + 7 - 10 + ..... + 2995 - 2998
Tính giá trị biểu thức:
A = 1-3+5-7+9-11+13-15+...+97-99+101
B=1-2-3-4+5-6-7-8+9-10-11-12+...+97-98-99-100
tính tổng:
1+2+3-4-5-6+7+8+9-10-11-12+.....+97+98+99-100-101-102
con nay la 1209876
111111111111000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000%
(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
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
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
1+2+3-4-5-6+7+8+9-10-11-12+...+97+98+99-100-101-102