Gửi h/ả hả bn ở dưới

a) Có: \(\overline{6\cdot7}⋮3\)

\(\Rightarrow6+7+\cdot⋮3\)

\(\Rightarrow13+\cdot⋮3\)

\(\Rightarrow\cdot\in\left\{2;5;8\right\}\)

b) Có: \(\overline{1\cdot8}⋮9\)

\(\Rightarrow1+8+\cdot⋮9\)

\(\Rightarrow9+\cdot⋮3\)

\(\Rightarrow\cdot\in\left\{0;9\right\}\)

\(\left(2x+3\right)\left(x-9\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}2x+3=0\\x-9=0\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=-\dfrac{3}{2}\\x=9\end{matrix}\right.\)

Vậy...

\(\dfrac{9}{11}+\dfrac{1}{12}:\dfrac{11}{24}=\dfrac{9}{11}+\dfrac{1}{12}\times\dfrac{24}{11}=\dfrac{9}{11}+\dfrac{2}{11}=1\)

Có: \(\dfrac{12}{48}< \dfrac{13}{48},\dfrac{13}{48}< \dfrac{13}{47}\Rightarrow\dfrac{12}{48}< \dfrac{13}{47}\)

Gọi số đó là `a`

\(\left\{{}\begin{matrix}a:5\left(dư1\right)\\a:7\left(dư3\right)\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}a+4⋮5\\a+4⋮7\end{matrix}\right.\)

\(\Rightarrow a+4\in BC\left(5;7\right)\)

mà \(\left(5;7\right)=1\Rightarrow BCNN\left(5;7\right)=5.7=35\)

\(\Rightarrow a=35-4=31\)

`42xxx+15xxx+43xxx=4000`

`=> x(42+15+43)=4000`

`=> 100x=4000`

`=> x=40`

Đây

\(\dfrac{25}{30}=1-\dfrac{5}{30}=1-\dfrac{1}{6}\)

\(\dfrac{40}{48}=1-\dfrac{8}{48}=1-\dfrac{1}{6}\)

\(\Rightarrow\dfrac{25}{30}=\dfrac{40}{48}\)

\(\dfrac{25}{30}=\dfrac{25:5}{30:5}=\dfrac{5}{6}\)

\(\dfrac{40}{48}=\dfrac{40:8}{48:8}=\dfrac{5}{6}=\dfrac{5}{6}=\dfrac{25}{30}\)

Có: \(3^{24}=3^4.3^4.3^4.3^4.3^4.3^4\)

\(\Rightarrow3^{24}=81.81.81.....81\)

\(\Rightarrow3^{24}=\overline{...1}\)

\(\Rightarrow B=\overline{...1}-2022^0=\overline{...1}-1=\overline{...0}\)