tự làm là hạnh phúc của mỗi công dân.
\(\frac{4}{2.4}+\frac{4}{4.6}+\frac{4}{6.8}+...+\frac{4}{2014.2016}\)
\(=2.\left(\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+...+\frac{2}{2014.2016}\right)\)
\(=2.\left(\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+...+\frac{1}{2014}-\frac{1}{2016}\right)\)
\(=2.\left(\frac{1}{2}-\frac{1}{2016}\right)\)
\(=2.\frac{1007}{2016}\)
\(=\frac{1007}{1008}\)
4/2*4 + 4/4*6 + 4/6*8 + ...+ 4/2014*2016
4/2*4 + 4/4*6 + 4/6*8 + ...+ 4/2014*2016
\(\frac{4}{2 . 4} + \frac{4}{4 . 6} + \frac{4}{6 . 8} + ... + \frac{4}{2012 . 2014} + \frac{4}{2014 . 2016}\) = ?
A=1-2+3+4-5-6+7+8-9-...+2007+2008-2009-2010
B=-1-2+3+4-5-6+7+8-9-10+11+12-...-2013-2014+2015+2016
C=(2+4+6+8+...+2014)-(3+5+7+9...+2011)
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
Tính nhanh:
1) A = 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + ... + 17 + 18 - 19 - 20
2) B = 1 - 2 - 3 + 4 + 5 - 6 - 7 + 8 + ... + 2013 - 2014 - 2015 + 2016
3) D = 4/13 + 4/3x5 + 4/5x7 + ... + 4/2013x2015
B= (-2)+4+(-6)+8+...+(-2014)+2016
tính :
B = 2 - 4 + 6 - 8 +..... - 2010 +2002
A = 1 + 2 - 3 + 4 + 5 + 6 - 7 - 8 + 9 + 10 + .+ 2013+ 2014- 2015 - 2016
2 + (- 4) + 6 + (-8) + 10 + ( -12) +......+2014 + ( - 2016) + 2018
