tính nhanh
A=1+3-5+7-..........-2013+2015
B=1-2+3-4+...................2015-2016
C=1-2-3+4+5-6-6+8+...........+2013-2014-2015+2016
D=1-4+7-10+.....-2014+2017
E=1+2-3-3+5+6 -.......+2013+2014-2015-2016
F=1-2+3-4+..........+2015+2016
G=1+3-5-7+9+11.............-2013-2015
H=1-2-34+5-6-7+8+.................+1013-1014-1015+1016
(1/2+2015/2016+2016/2017+1)(2015/2016+2016/2017+7/22)-(1/2+2015/2016+2016/2017)(2015/2016+2016/2017+7/22+1)
cho S= 1+7+7^2+7^3+...+7^2015
CMR: 6S+1=7^2016
(1/2+2015/2016+216/2017+1)(2015/2016+2016/2017+7/22)-(1/2+2015+2016)(2015/2016+2016/2017+7/22+1)
Tính
(1/2 + 2015/2016 + 2016/2017 + 1)(2015/2016 + 2016/2017 + 7/22) - (1/2 + 2015/2016 + 2016/2017)(2015/2016 + 2016/2017 + 7/22 + 1)
A=7 mu 2020 mu 2019-3 mu 2016 mu 2015 :5 chung to A la so chan
Cho A=1 + 7^1 + 7^1 + 7^2 + 7^3 + 7^4 +... + 7^2015
chứng minh a chia hết cho 8
Giúp mk với
(1/2+2015/2016+2016/2017+1)(2015/2016+2016/2017+7/22)-(1/2+2015/2016+2016/2017)(2015/2016+2016/2017+7/22+1)
Chứng tỏ :
a) 5^2017+5^2016+5^2015 chia hết cho 31
b) 1+7+7^2+7^3+...+7^101 chia hết cho 8
