=5/7*1/21

=5/147

5/7 x 7 - 2/14 x7 +7 

= 5/7 x 7/1 - 2/14 x 7/1 +7

= -1

7x(2-5/7+14)

7x23

141

\(\dfrac{-1}{9}.\dfrac{-3}{5}+\dfrac{5}{-6}.\dfrac{-3}{5}-\dfrac{7}{2}.\dfrac{3}{5}\)

\(=\dfrac{3}{5}.\left(\dfrac{1}{9}+\dfrac{5}{6}-\dfrac{7}{2}\right)\)

\(=\dfrac{3}{5}.\left(\dfrac{2}{18}+\dfrac{15}{18}-\dfrac{63}{18}\right)\)

\(=\dfrac{3}{5}.\left(-\dfrac{23}{9}\right)\)

\(=-\dfrac{69}{45}\)

1-2+3-4+5-6+7-8+9-10+11=(-1)+(-1)+(-1)...+(-1)+11

                                      =(-1).5+11

                                      =(-5)+11

                                      =6

1-2+3-4+5-6+7-8+9-10+11=6

1-2

1-2

1-2+3-4+5-6+7-8+9-10+11=6

`1/5 . 4/7 + 3/7 . 1/5 -1/5`

`=1/5 . 4/7 + 3/7 . 1/5 -1/5 . 1`

`=1/5 . ( 4/7+3/7-1)`

`=1/5 . ( 7/7-1)`

`= 1/5 . 0`

`=0`

\(\dfrac{1}{5}\times\dfrac{4}{7}+\dfrac{3}{7}\times\dfrac{1}{5}-\dfrac{1}{5}=\dfrac{1}{5}\times\left(\dfrac{4}{7}+\dfrac{3}{7}-1\right)=\dfrac{1}{5}\times0=0\)

= \(\dfrac{1}{5}\).(\(\dfrac{4}{7}\)+\(\dfrac{3}{7}\)+1)

= \(\dfrac{1}{5}\)+ 0

\(\dfrac{1}{5}\)

`2/5 - 3/8 + 7/6 : 7/5`

`= 2/5 - 3/8 + 7/6 xx 5/7`

`= 2/5 - 3/8 +5/6`

`= 1/40+5/6`

`=103/120`

2870 đó bạn

Mk yêu cầu tính nhe bạn

tu tinh đã có kết qủa rồi lai còn 

A= 1 + 2 - 3 - 4 + 5 + 6 - 7 - 8 + 9 +...+ 2013 + 2014 - 2015 - 2016

A= 3 - 7 + 11 - 15 +...+ 4027 - 4031

A= -3 + -3 + -3 +...+ -3 + -3

A= -3 × 1008 = -3024

bạn nguyễn lương phương thảo bạn đã làm sai rồi bước thứ hai phải là "-4" chứ

\(a,\frac{21}{11}\cdot\frac{22}{17}\cdot\frac{68}{63}=\frac{21\cdot22\cdot68}{11\cdot17\cdot63}=\frac{21\cdot11\cdot2\cdot17\cdot4}{11\cdot17\cdot21\cdot3}=\frac{8}{3}\)

\(b,\frac{5}{14}\cdot\frac{7}{13}\cdot\frac{26}{25}=\frac{5\cdot7\cdot26}{14\cdot13\cdot25}=\frac{5\cdot7\cdot13\cdot2}{7\cdot2\cdot13\cdot5\cdot5}=\frac{1}{5}\)

a)  \(\frac{21}{11}\times\frac{22}{17}\times\frac{68}{63}=\frac{21\times22\times68}{11\times17\times63}\)

\(=\frac{21\times2\times11\times4\times17}{11\times17\times3\times21}\)

\(=\frac{8}{3}\)

b)  \(\frac{5}{14}\times\frac{7}{13}\times\frac{26}{25}=\frac{5\times7\times26}{14\times13\times25}\)

\(=\frac{5\times7\times2\times13}{2\times7\times13\times5\times5}\)

\(=\frac{1}{5}\)

dấu chấm là gì vậy bạn cô gái

 cô đơn

Bài 1: Tính
a, 1/2 x 2/3 x 3/4 = 1/4
b, 7/8 x 8/9 x 9/10 = 7/10
c, 5/14 x 7/15 x 28/7 = 2/3
d, 2 x 1/2 x 3 x 1/3 x 4 x 1/4 x 5 x 1/5 = 1
Bài 2: Tính
a, 7/20 - ( 5/8 - 3/5 ) = 7/20 - 1/40 = 14/40 - 1/40 = 13/40
b, 5/6 + ( 5/9 - 1/4 ) = 5/6 + 11/36 = 30/36 + 11/36 = 41/36
c, 9/10 - ( 2/5 + 3/10 ) + 7/20 = 9/10 - 7/10 + 7/20 = 2/10 + 7/20 = 4/20 + 7/20 = 11/20.
Bài 3: Tìm x:
a, 1/2 + x = 5/6
x = 5/6 - 1/2
x = 1/3
b, 5/6 - x = 1/3
x = 5/6 - 1/3
x = 1/2
c, x - 1/mấy vậy bạn
d, 1/3 x x = 1/6
x = 1/6 : 1/3
x = 1/2