bài 7:

(9:9)+(9-9)+9=10

(9+9)-9+(9:9)=10

9x9:9+(9:9)=10

bài 9 

76 + 8 + 5 + 9 + 2 - 4 + 3  + 1 = 100 

nha bạn 

Bài 9:76+8+5+9+2-4+3+1=100

\(\dfrac{200x}{100}+\dfrac{300\left(x-20\right)}{100}=\dfrac{33.500}{100}\)

=> 200x + 300(x - 20) = 16500

<=> 200x + 300x - 6000 = 16500

<=> 500x = 22500

<=> x = 45

S = {45}

Ta có: \(\dfrac{x\cdot200}{100}+\dfrac{\left(x-20\right)\cdot300}{100}=\dfrac{33\cdot500}{100}\)

\(\Leftrightarrow200x+300x-6000=16500\)

\(\Leftrightarrow500x=22500\)

hay x=45

Vậy: S={45}

đề?

it ở đây là dg chỉ cái j

It will be wonderful.

\(\frac{5}{2}-\frac{1}{3}\div\frac{1}{6}=\frac{5}{2}-2=\frac{1}{2}\)

5/2 - (1/3 x 6/1) = 5/2 - 6/3 = 5/2 - 2= 1/2

-HT-

TL:

5/2-1/3:1/6

\(\frac{5}{2}\)- \(\frac{1}{3}\): \(\frac{1}{6}\)= \(\frac{5}{2}\)- 2 =\(\frac{1}{2}\)

-HT-

\(A=\left(n+1\right)\left(n-1+1\right):2\)

mình thấy người ta bảo là bằng 2031120 . các bạn cho mình cách giải 

Có công thức nhé :) 

Số số hạng : \(\frac{2015-1}{2}+1=1008\) ( số hạng ) 

Tổng : \(\frac{\left(2015+1\right).2008}{2}=1016064\)

Vậy \(A=1016064\)

Chúc bạn học tốt ~ 

1016065

\(=\dfrac{1}{3}:\dfrac{7\cdot\left(5+3\right)}{18\cdot\left(53-11\right)}\) 

\(=\dfrac{1}{3}:\dfrac{7\cdot8}{18\cdot42}\) 

\(=\dfrac{1}{3}:\dfrac{7\cdot2\cdot2\cdot2}{3\cdot3\cdot2\cdot2\cdot3\cdot7}\)

\(=\dfrac{1}{3}:\dfrac{2}{3\cdot3\cdot3}\)

\(=\dfrac{1}{3}\cdot\dfrac{27}{2}\)

\(=\dfrac{9}{2}\)

`1/15+1/35+1/63+1/99+1/143`

`=1/[3.5]+1/[5.7]+1/[7.9]+1/[9.11]+1/[11.13]`

`=1/2(2/[3.5]+2/[5.7]+2/[7.9]+2/[9.11]+2/[11.13])`

`=1/2.(1/3-1/5+1/5-1/7+...+1/11-1/13)`

`=1/2.(1/3-1/13)`

`=1/2 . 10/39`

`=5/39`

`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

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