cau hỏi tương tự ko có mà!!!!!!!!!!!!!!!!!!!!!!!!!!!!

3C=1.2.3+2.3.(4-1)+3.4.(5-2)+...+2014.2015.(2016-2013)

3C=2014.2015.2016

C=2014.2015.2016:3

D=673015

E=2550

C=...

G=781875

lấy lời giải ra hộ  tui

D=1+4+7+...+2008
D=(2008-1):3+1
D=670.
VẬY D=670.
E=2+4+6+...+100
E=(100-2):2+1
E=49.
VẬY E=49.
C=2+4+6+...+1024
C=(1024-2):2+1
C=512.
VẬY C=512.
 

\(S=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+.......+\frac{1}{2015.2016}\)

\(S=\frac{1}{1}-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+.......+\frac{1}{2015}-\frac{1}{2016}\)

\(S=\frac{1}{1}-\frac{1}{2016}=\frac{2015}{2016}\)

làm r sao cứ đăng hoài vậy?

S=1/1-1//2+1/2-1/3+1/3-1/4+.......=1/2014-1/2015

S=1/1-1/2015

S=2015/2015-1/2015

S=2014/2015

Đặt S = 1.2 + 2.3 + 3.4 + ... + 2013.2014 
3S = 1.2.3 + 2.3.3 + 3.4.3 + ... + 2013.2014.3 
Mà : 
1.2.3 = 1.2.3 
2.3.3 = 2.3.4 - 2.3.1 
3.4.3 = 3.4.5 - 3.4.2 
................................... 
................................... 
2012.2013.3 = 2012.2013.2014 - 2012.2013.2011 
2013.2014.3 = 2013.2014.2015 - 2013.2014.2012 
Cộng tất cả, vế theo vế ---> 3S = 2013.2014.2015 
---> S = 2013.2014.2015 / 3 = 2723058910

A=1.2+2.3+....+2014.2015

=>3A=1.2.3+2.3.3+3.4.3+...+2015.2014.3

=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+...+2014.2015.(2016-2013)

=1.2.3-0.1.2+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+.....+2014.2015.2016-2013.2014.2015

=(1.2.3-1.2.3)+(2.3.4-2.3.4)+(3.4.5-3.4.5)+....+(2013.2014.2015-2013.2014.2015)+0.1.2+2013.2014.2015

=0+2013.2014.2015

=>A=\(\frac{2013.2014.2015}{3}\)

A=1.2+2.3+3.4+4.5+...+2014.2015

=>3A=1.2.3+2.3.3+3.4.3+4.5.3+...+2014.2015.3

=1.2.(3-0)+2.3.(4-1)+3.4.(5-2)+4.5.(6-3)+...+2014.2015.(2016-2013)

=1.2.3-0.1.2+2.3.4-1.2.3+3.4.5-2.3.4+4.5.6-3.4.5+...+2014.2015.2016-2013.2014.2015

=(1.2.3-1.2.3)+(2.3.4-2.3.4)+(3.4.5-3.4.5)+(4.5.6-4.5.6)+...+(2013.2014.2015-2013.2014.2015)+0.1.2+2014.2015.2016

=0+2014.2015.2016

=>A=\(\frac{2014.2015.2016}{3}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{2014}-\frac{1}{2015}\)

\(=1-\frac{1}{2015}\)

\(=\frac{2014}{2015}\)

A=1/1-1/2+1/2-1/3+1/3-...........+1/2014-1/2015

A=1/1-1/2015

A=2014/2015

\(A=4\left(1-\dfrac{1}{2}+\dfrac{1}{2}-\dfrac{1}{3}+...+\dfrac{1}{2014}-\dfrac{1}{2015}\right)\)

\(=4\cdot\dfrac{2014}{2015}=\dfrac{8056}{2015}\)