Đặt A\(=\)\(2^0+2^1+2^2+.........+2^{2020}\)

\(\Rightarrow\)2A\(=\)\(2^1+2^2+2^3+.......+2^{2021}\)

\(\Rightarrow\)2A - A \(=\) (\(2^1+2^2+2^3+.....+2^{2021}\))\(-\)(\(2^0+2^1+2^2+.....+2^{2020}\))

\(\Rightarrow\)A \(=2^{2021}-2^0\)

\(\Rightarrow\)A \(=\)\(2^{2021}-1\)

3/4x7+6/7x13+10/13x23+1/23x24+4/24/28

=7-4/4x7+13-7/7x13+…+28-24/24x28

=1/4-1/7+1/7-1/13+…+1/24-1/28

=1/4-1/28

=3/14

Sera Phim sans chúc bạn học tốt

\(B=\frac{3}{4.7}+\frac{6}{7.13}+\frac{10}{13.23}+\frac{1}{23.24}+\frac{4}{24.28}\)

\(=\frac{1}{4}-\frac{1}{7}+\frac{1}{7}-\frac{1}{13}+\frac{1}{13}-\frac{1}{23}+\frac{1}{23}-\frac{1}{24}+\frac{1}{24}-\frac{1}{28}=\frac{1}{4}-\frac{1}{28}=\frac{3}{14}\)

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{49.50}\)

\(=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}=1-\frac{1}{50}=\frac{49}{50}\)

\(A=\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+....+\frac{1}{49.50}\)

\(A=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{49}-\frac{1}{50}\)

\(A=1-\left(-\frac{1}{2}+\frac{1}{2}\right)-\left(-\frac{1}{3}+\frac{1}{3}\right)-\left(-\frac{1}{4}+\frac{1}{4}\right)+...+\left(-\frac{1}{49}+\frac{1}{49}\right)-\frac{1}{50}\)

\(A=1-\frac{1}{50}\)

\(A=\frac{49}{50}\)

mk làm đc nhưng mà bài nhiều quá

HƠI DÀI

Chiều rộng mảnh vườn:

100:\(\frac{5}{2}\) = 20(m)

Đ/s:.............

Cho \(A=\frac{2n+2}{2n-4}=\frac{2n-4+6}{2n-4}=\frac{2n-4}{2n-4}+\frac{6}{2n-4}=1+\frac{6}{2n-4}\)

a, Để A là phân số thì \(2n-4\ne0\Rightarrow2n\ne4\Rightarrow n\ne2\)

b, Để A nguyên \(\Rightarrow6⋮2n-4\)hay \(2n-4\inƯ\left(6\right)\)

\(Ư\left(6\right)\in\left\{\pm1;\pm2;\pm3;\pm6\right\}\)

Vậy để A nguyên thì \(n\in\left\{3;1;5;-1\right\}\)

\(\frac{3}{7}.5-9=\frac{3x+52}{x}+16\frac{1}{7}\)

\(\Leftrightarrow\frac{15}{7}-9=\frac{3x}{x}+\frac{52}{x}+\frac{113}{7}\)

\(\Leftrightarrow-\frac{48}{7}=3+\frac{52}{x}+\frac{113}{7}\)

\(\Leftrightarrow-\frac{48}{7}-3-\frac{113}{7}=\frac{52}{x}\)

\(\Leftrightarrow-26=\frac{52}{x}\)

\(\Leftrightarrow\left(-26\right).x=52\)

\(\Rightarrow x=-2\)