-5/21 nhé bn

\(1\dfrac{13}{15}\cdot0,75-\left[\dfrac{11}{20}+25\%\right]\div\dfrac{7}{5}\\ =\dfrac{28}{15}\cdot0,75-\dfrac{4}{5}\cdot\dfrac{5}{7}\\ =\dfrac{7}{5}-\dfrac{4}{7}=\dfrac{29}{35}\)

Biểu đồ đâu bạn?

Đề bài đâu bạn?

4a.

$A=\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+....+\frac{1}{2^{100}}$

$2A=1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{99}}$

$\Rightarrow 2A-A=(1+\frac{1}{2}+\frac{1}{2^2}+...+\frac{1}{2^{99}})-(\frac{1}{2}+\frac{1}{2^2}+\frac{1}{2^3}+....+\frac{1}{2^{100}})$

$\Rightarrow A=1-\frac{1}{2^{100}}$

4b.

$B=1+\frac{1}{3}+\frac{1}{3^2}+....+\frac{1}{3^{100}}$

$3B=3+1+\frac{1}{3}+...+\frac{1}{3^{99}}$

$\Rightarrow 3B-B=(3+1+\frac{1}{3}+...+\frac{1}{3^{99}})-(1+\frac{1}{3}+\frac{1}{3^2}+....+\frac{1}{3^{100}})$

$\Rightarrow 2B=3-\frac{1}{3^{100}}$

$\Rightarrow B=\frac{3}{2}-\frac{1}{2.3^{100}}$

em ơi chưa có bài em nhé, em chưa tải bài lên lám sao mình giúp được 

Dạ đề đây ạ   

`(3*x+2)^2=121`

\(=>\left[{}\begin{matrix}3x+2=11\\3x+2=-11\end{matrix}\right.\\ =>\left[{}\begin{matrix}3x=11-2\\3x=-11-2\end{matrix}\right.\\ =>\left[{}\begin{matrix}3x=9\\3x=-13\end{matrix}\right.\\ =>\left[{}\begin{matrix}x=3\left(tm\right)\\x=-\dfrac{13}{3}\left(loại\right)\end{matrix}\right.\)

`(3x+2)^2=121`

`=>( 3x+2)^2= +-11^2`

\(\Rightarrow\left[{}\begin{matrix}3x+2=11\\3x+2=-11\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}3x=9\\3x=-13\end{matrix}\right.\)

\(\Rightarrow\left[{}\begin{matrix}x=3\\x=-\dfrac{13}{3}\end{matrix}\right.\)

\(A=1+\dfrac{1}{8}+\dfrac{1}{24}+\dfrac{1}{48}+\dfrac{1}{80}+\dfrac{1}{120}\)

\(=1+\dfrac{1}{2\times4}+\dfrac{1}{4\times6}+\dfrac{1}{6\times8}+\dfrac{1}{8\times10}+\dfrac{1}{10\times12}\)

\(=1+\dfrac{1}{2}-\dfrac{1}{4}+\dfrac{1}{4}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{10}+\dfrac{1}{10}-\dfrac{1}{12}\)

\(=1+\dfrac{1}{2}-\dfrac{1}{12}=\dfrac{17}{12}\)