1+1=2

2+2=4

3+3=6

Hok-Tốt

@Thiên_Hy

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\(A=1+3+3^2+.....+3^{11}\)

\(A=\left(1+3+3^2\right)+....+\left(3^9+3^{10}+3^{11}\right)\)

\(A=\left(3^0.1+3^0.3+3^0.3^2\right)+....+\left(3^9.1+3^9.3+3^9.3^2\right)\)

\(A=1.\left(1+3+3^2\right)+....+3^9\left(1+3+3^2\right)\)

\(A=1.13+....+3^9.13\)

\(A=13.\left(1+....+3^9\right)⋮13\left(đpcm\right)\)

Cảm ơn bạn nhé!

k mk mk k lai cho

phép tính do các bạn đặt ra 

tùy

2+3=5

MAGICPENCIL K MIK NHA PLEASE MIK SẼ K LẠI

hứa 

A= 1/3+1/6+1/10+...+1/561

  = 2. (1/6+1/12+1/20+...+1/1122)

  = 2. [1/(2.3) + 1/(3.4) + 1/(4.5) +...+1/(33.34)]

  = 2. ( 1/2 - 1/3 +1/3 - 1/4 + 1/4 - 1/5 +...+ 1/33 - 1/34 )

  =2. (1/2 - 1/34)

  =2. 8/17

  =16/17

Vì 16/17 > 16/18 = 8/9 -> A > 8/9

dễ 4nha

\(\Leftrightarrow\orbr{\begin{cases}x+\frac{2}{7}=\frac{1}{6}\\x+\frac{2}{7}=\frac{-1}{6}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{-5}{42}\\x=\frac{-19}{42}\end{cases}}\)

Vậy ...

 Ta có: \(\left|x+\frac{2}{7}\right|=\frac{1}{6}\)

\(\Rightarrow\orbr{\begin{cases}x+\frac{2}{7}=\frac{1}{6}\\x+\frac{2}{7}=-\frac{1}{6}\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{1}{6}-\frac{2}{7}=-\frac{5}{42}\\x=-\frac{1}{6}-\frac{2}{7}=-\frac{19}{42}\end{cases}}\)

Vậy \(x\in\left\{-\frac{5}{42};-\frac{19}{42}\right\}\)

~Study well~

20 phút nữa what

2x+2x=4x

3x+6x-7x=2x

5x+45x=50x