= -101/100

\(B=-\frac{1}{1.2}-\frac{1}{2.3}-\frac{1}{3.4}-...-\frac{1}{98.99}-\frac{1}{99.100}\\ =-\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{98.99}+\frac{1}{99.100}\right)\\ =-\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{98}-\frac{1}{99}+\frac{1}{99}-\frac{1}{100}\right)\\ =-\left(1-\frac{1}{100}\right)=\frac{-99}{100}\)

<br class="Apple-interchange-newline"><div></div>B=−11.2 −12.3 −13.4 −...−198.99 −199.100  \\ =−(11.2 +12.3 +13.4 +...+198.99 +199.100 ) \\ =−(1−12 +12 −13 +13 −14 +...+198 −199 +199 −1100 ) \\ =−(1−1100 )=−99100 

có lỗi ko

Ta có : A = 1.2 + 2.3 + 3.4 + ..... + 49.50

=> 3A = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + .... + 49.50.51

=> 3A = 49.50.51

= >A = 49.50.51/3 = 41650

3A= 1.2.3 + 2.3.(4-1) +3.4.(5-2) +...+ 99.100.(101-98)

3A= 1.2.3 + 2.3.4 - 1.2.3 + 3.4.5 - 2.3.4 +...+-99.100.98

3A=99.100.101

A= 33.100.101

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

Ta có : S = 1.2 + 2.3 + 3.4 + ..... + 32.33

=> 3S = 1.2.3 - 1.2.3 + 2.3.4 - 2.3.4 + ...... + 32.33.34

=> 3S = 32.33.34

=> S = \(\frac{32.33.34}{3}=11968\)

C=1*2+2*3+3*4+...+98*99

C=2+6+12+...+9702

C=2+9702

C=9704

vay C=9704

D=(1*99+2*99+3*99+...+99*99)-(1*2+2*3+3*4+...+98*99)

D=(99+198+297+...+9801)-(2+6+12+...+9702)

D=(99+9801)-(2+9702)

D=9900-9704

D=196

vay D=196

ai di qua dong tinh thi nho h cho minh nhe

Đug r pn

có cần chi tiết hơn k

\(\left(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+..+\frac{1}{49.50}\right)x=\frac{49}{50}\)

\(\left(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+...+\frac{1}{49}-\frac{1}{50}\right)x=\frac{49}{50}\)

\(\left(1-\frac{1}{50}\right)x=\frac{49}{50}\)

\(\frac{49}{50}x=\frac{49}{50}\)

\(x=\frac{\frac{49}{50}}{\frac{49}{50}}\)

\(x=1\)

Vậy \(x=1\)

Gọi A=1/1.2+1/2.3+1/3.4+...+1/49.50

A=1-1/2+1/2-1/3+1/3-1/4+...+1/49-1/50

A=1-1/50

A=49/50

Viết lại ta có: (1/1.2+1/2.3+1/3.4+...+1/49.50)x=49/50

                 49/50x=49/50

               => x=1

sai đề 

sai đề là cái chắc

sai đề hả bạn????

3S=1.2.3+2.3.3+3.4.3+...+49.50.3
=1.2.3+2.3.(4-1)+3.4.(5-2)+...+48.49.(50-47)+49.50.(51-48)
=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+48.49.50-47.48.49+49.50.51-48.49.50
=(1.2.3-1.2.3)+(2.3.4-2.3.4)+...(47.48.49-47.48.49)-(48.49.50-48.49.50)+49.50.51
=0+0+...+0+0+49.50.51
=49.50.51
S=(49.50.51)/3
=41650
Đáp số:41650

lê thị ngọc anh trả lời đúng đấy tin bạn ấy đi

3S=1.2.3+2.3.3+3.4.3+...+49.50.3

=1.2.3+2.3.(4-1)+3.4.(5-2)+...+48.49.(50-47)+49.50.(51-48)

=1.2.3+2.3.4-1.2.3+3.4.5-2.3.4+...+48.49.50-47.48.49+49.50.51-48.49.50

=(1.2.3-1.2.3)+(2.3.4-2.3.4)+...(47.48.49-47.48.49)-(48.49.50-48.49.50)+49.50.51

=0+0+...+0+0+49.50.51

=49.50.51

S=(49.50.51)/3

=41650