<=> {[(2x-2):2+1]:2}.(2x+2) =210
<=> {[2(x-1):2+1]:2}.2(x+1) =210
<=> [(x-1)+1]:2.2(x+1) =210
<=> (x-1+1)(x+1) =210
<=> x(x+1) =210
Vì 14.15=210 nên x=14

( ko chắc)

ab=cd

6.8=24.x

6.24=8.y

8.24=6.z

     Số cần tìm là 12.

          12 x 11 = 132

số đó là 12 

12 x 11 = 132 ( các số có hai chữ số nhân với 11 )

\(\Leftrightarrow4-\left(\frac{7}{3}-x+\frac{1}{4}\right)=1-\left|\frac{7}{6}-\frac{29}{12}\right|+\frac{3}{12}.\)

\(\Leftrightarrow4-\frac{31}{12}+x=1-\left|\frac{-15}{12}\right|+\frac{3}{12}\)

\(\Leftrightarrow\frac{17}{12}+x=1-\frac{15}{12}+\frac{3}{12}\)

\(\Leftrightarrow\frac{17}{12}+x=0\Leftrightarrow x=\frac{-17}{12}\)

\(4-\left(2\frac{1}{3}-x+\frac{1}{4}\right)=1-|1\frac{1}{6}-2\frac{5}{12}|+1\frac{1}{2}\)

\(4-\left(2\frac{1}{3}-x+\frac{1}{4}\right)=1+\frac{5}{4}+\frac{3}{2}\)

\(4-\left(\frac{7}{3}-x+\frac{1}{4}\right)=\frac{4+5+6}{4}\)

\(4-\left(\frac{7}{3}-x+\frac{1}{4}\right)=\frac{15}{4}\)

\(\frac{7}{3}-x+\frac{1}{4}=4-\frac{15}{4}\)

\(\frac{31}{12}-x=\frac{1}{4}\)

\(x=\frac{31}{12}-\frac{1}{4}=\frac{7}{3}\)

a) \(\frac{1}{3}+\frac{2}{3}:x=-7\)

=> \(\frac{2}{3}:x=-7-\frac{1}{3}\)

=> \(\frac{2}{3}:x=-\frac{22}{3}\)

=> \(x=\frac{2}{3}:\left(-\frac{22}{3}\right)\)

=> \(x=-\frac{1}{11}\)

b) \(\frac{1}{3}x+\frac{2}{5}x=0\)

=> \(\frac{11}{15}x=0\)

=> \(x=0\)

c) \(\left(2x-3\right)\left(6-2x\right)=0\)

=> \(\left(2x-3\right)\left(3-x\right).2=0\)

=> \(\left(2x-3\right)\left(3-x\right)=0\)

=> \(\orbr{\begin{cases}2x-3=0\\3-x=0\end{cases}}\)

=> \(\orbr{\begin{cases}x=\frac{3}{2}\\x=3\end{cases}}\)

a) \(\frac{1}{3}+\frac{2}{3}:x=-7\)

\(\Rightarrow\frac{2}{3}.\frac{1}{x}=-7-\frac{1}{3}\)

\(\Rightarrow\frac{2}{3x}=\frac{-21-1}{3}\)

\(\Rightarrow\frac{2}{3x}=\frac{-22}{3}\)

\(\Rightarrow-22.3x=6\)

\(\Rightarrow3x=\frac{-6}{22}=\frac{-3}{11}\)

\(\Rightarrow x=\frac{-3}{11}:3=\frac{-3}{11}.\frac{1}{3}\)

\(\Rightarrow x=\frac{-1}{11}\)

b) \(\frac{1}{3}x+\frac{2}{5}x=0\)

\(\Rightarrow x.\left(\frac{1}{3}+\frac{2}{5}\right)=0\)

\(\Rightarrow x=0\)

c) \(\left(2x-3\right).\left(6-2x\right)=0\)

\(\Rightarrow\orbr{\begin{cases}2x-3=0\\6-2x=0\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}2x=3\\2x=6\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{3}{2}\\x=3\end{cases}}\)

d) \(x:\frac{3}{4}+\frac{1}{4}=\frac{-2}{3}\)

\(\Rightarrow x.\frac{4}{3}=\frac{-2}{3}-\frac{1}{4}\)

\(\Rightarrow x.\frac{4}{3}=\frac{-11}{12}\)

\(\Rightarrow x=\frac{-11}{12}:\frac{4}{3}=\frac{-11}{12}.\frac{3}{4}=\frac{-11}{16}\)

e) \(\frac{3}{4}-\left|x-\frac{2}{3}\right|=\frac{1}{2}\)

\(\Rightarrow\left|x-\frac{2}{3}\right|=\frac{3}{4}-\frac{1}{2}\)

\(\Rightarrow\left|x-\frac{2}{3}\right|=\frac{1}{4}\)

\(\Rightarrow\orbr{\begin{cases}x-\frac{2}{3}=\frac{1}{4}\\x-\frac{2}{3}=\frac{-1}{4}\end{cases}}\)

\(\Rightarrow\orbr{\begin{cases}x=\frac{11}{12}\\x=\frac{5}{12}\end{cases}}\)

A = 2 + 2² + 2³ + ... + 2²⁰¹⁰

=> 2A = 2² + 2³ + 2⁴ + ... + 2²⁰¹¹

Lấy 2A - A = (2² + 2³ + 2⁴ + ... + 2²⁰¹¹) - (2 + 2² + 2³ + .... + 2²⁰¹⁰)

              A  = 2² + 2³ + 2⁴ + ... + 2²⁰¹¹ - 2 - 2² - 2³ - .... - 2²⁰¹⁰

                  = 2²⁰¹¹ - 2

=> A = 2²⁰¹¹ - 2