\(\Rightarrow\frac{2\chi-3}{5}=1-\frac{\chi}{7}\)

\(\Rightarrow\frac{2\chi-3}{5}=\frac{7-\chi}{7}\)

\(\Rightarrow\frac{2\chi-3-7-\chi}{5-7}\Rightarrow\frac{\chi-10}{-2}\)

\(\Leftrightarrow\chi-10\in\)Ư(-2)

DEN day ban tu giai nha

HTDT

\(\frac{2x-3}{5}+\frac{x}{7}=1\)

\(\Rightarrow\frac{14x-21}{35}+\frac{5x}{35}=\frac{35}{35}\)

\(\Rightarrow14x-21+5x=35\)

\(\Rightarrow14x+5x=35+21=56\)

\(\Rightarrow19x=56\)

\(\Rightarrow x=\frac{56}{19}\)

\(\left|2x+7\right|-\left|5x+4\right|=0\)

\(\Leftrightarrow\)\(\left|2x+7\right|=\left|5x+4\right|\)

\(\Leftrightarrow\)\(\orbr{\begin{cases}2x+7=5x+4\\2x+7=-5x-4\end{cases}\Leftrightarrow\orbr{\begin{cases}5x-2x=7-4\\2x+5x=-4-7\end{cases}\Leftrightarrow}\orbr{\begin{cases}3x=3\\7x=-11\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=1\\x=\frac{-11}{7}\end{cases}}}\)

... 

\(\left|2x+7\right|-\left|5x+4\right|=0\)

\(\Rightarrow\left|2x+7\right|=\left|5x+4\right|\)

\(\Rightarrow\hept{\begin{cases}2x+7=5x+4\\2x+7=-5x+4\end{cases}}\Rightarrow\hept{\begin{cases}5x-2x=7-4\\-5x-2x=7+4\end{cases}}\Rightarrow\hept{\begin{cases}3x=3\\-7x=11\end{cases}}\Rightarrow\hept{\begin{cases}x=1\\x=-\frac{11}{7}\end{cases}}\)

\(\text{Ta có : }2009^{20}=(2009^2)^{10}=(2009\cdot2009)^{10}\)

\(20092009^{10}=(2009\cdot10001)^{10}\)

\(\text{Vì }(2009\cdot2009)^{10}< (2009\cdot10001)^{10}\text{nên }2009^{20}< 20092009^{10}\)

Chúc bạn học tốt ~

Thanks TL

Ban nên sử dụng bất đẳng thúc cosi

a) x=7