Ta có:

A=2+2^2+2^3+....+2^99+2^100

=>2A=2^2+2^3+2^4+....+2^100+2^101

=>2A-A=(2^2+2^3+2^4+....+2^101)-(2+2^2+2^3+....+2^99)

Phá ngoặc ra, ta được:

A=2^101-2.

P/s:Nếu bạn có máy tính cầm tay, bấm 2^100-2 bằng bao nhiêu nhé !!!Chúc bạn học tốt.

Ta có : 

\(A=2+2^2+2^3+...+2^{100}\)

\(\Rightarrow2A=2^2+2^3+2^4+...+2^{101}\)

\(\Rightarrow2A-A=\left(2^2+2^3+2^4+...+2^{100}\right)-\left(2+2^2+2^3+...+2^{100}\right)\)

\(\Rightarrow A=2^{101}-2\)

Vậy \(A=2^{101}-2\)

cam on moi nguoi nhe

\(\left(\frac{2}{3}.x+\frac{5}{6}\right).\left(\frac{3}{4}.x-\frac{27}{8}\right)=0\)

\(\Rightarrow\orbr{\begin{cases}\frac{2}{3}.x+\frac{5}{6}=0\\\frac{3}{4}.x-\frac{27}{8}=0\end{cases}}\Rightarrow\orbr{\begin{cases}\frac{2}{3}.x=\frac{-5}{6}\\\frac{3}{4}.x=\frac{27}{8}\end{cases}}\Rightarrow\orbr{\begin{cases}x=\frac{-5}{4}\\x=\frac{9}{2}\end{cases}}\)

Vậy \(x=\frac{-5}{4}\) hoặc \(x=\frac{9}{2}\).

Học tốt

\(\left(\frac{2}{3}.x+\frac{5}{6}\right).\left(\frac{3}{4}.x-\frac{27}{8}\right)=0=>\orbr{\begin{cases}\left(\frac{3}{4}.x-\frac{27}{8}\right)=0\\\left(\frac{2}{3}.x+\frac{5}{6}\right)=0\end{cases}}\)

\(\orbr{\begin{cases}\frac{2}{3}.x=0-\frac{5}{6}\\\frac{3}{4}.x=0+\frac{27}{8}\end{cases}}=>\orbr{\begin{cases}\frac{2}{3}.x=-\frac{5}{6}\\\frac{3}{4}.x=\frac{27}{8}\end{cases}}=>\orbr{\begin{cases}x=-\frac{5}{6}:\frac{2}{3}\\x=\frac{27}{8}:\frac{3}{4}\end{cases}}=>\orbr{\begin{cases}x=-\frac{5}{4}\\x=\frac{9}{2}\end{cases}}\)

vậy \(\orbr{\begin{cases}x=-\frac{5}{4}\\x=\frac{9}{2}\end{cases}}\)

                Bài làm :

\(\left(\frac{2}{3}x+\frac{5}{6}\right).\left(\frac{3}{4}x-\frac{27}{8}\right)=0\)

\(\Leftrightarrow\orbr{\begin{cases}\frac{2}{3}x+\frac{5}{6}=0\\\frac{3}{4}x-\frac{27}{8}=0\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}\frac{2}{3}x=\frac{-5}{6}\\\frac{3}{4}x=\frac{27}{8}\end{cases}}\)

\(\Leftrightarrow\orbr{\begin{cases}x=\frac{-5}{4}\\x=\frac{9}{2}\end{cases}}\)

Vậy x=-5/4 hoặc x=9/2

a) Đặt \(A=\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\)

\(2A=\left(\frac{1}{2}\times2\right)+\left(\frac{1}{4}\times2\right)+\left(\frac{1}{8}\times2\right)+\left(\frac{1}{16}\times2\right)+\left(\frac{1}{32}\times2\right)\)

\(2A=1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}\)

Ta lấy : \(2A-1A=1A\)

\(A=\left(1+\frac{1}{2}+\frac{1}{4}+\frac{1}{8}+\frac{1}{16}\right)-\left(\frac{1}{2}+\frac{1}{4}+\frac{1}{6}+\frac{1}{8}+\frac{1}{16}+\frac{1}{32}\right)\)

\(A=1-\frac{1}{32}\)

\(A=\frac{31}{32}\)

Vậy \(A=\frac{31}{32}\)

b) Đặt \(B=\frac{2}{1\times2}+\frac{2}{2\times3}+\frac{2}{3\times4}+...+\frac{2}{18\times19}+\frac{2}{19\times20}\)

\(B=2\times(1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{18}-\frac{1}{19}+\frac{1}{19}-\frac{1}{20})\)

\(B=2\times\left(1-\frac{1}{20}\right)\)

\(B=2\times\frac{19}{20}\)

\(B=\frac{19}{10}\)

Vậy \(B=\frac{19}{10}\)

Học tốt # ^-<

dau gach cheo la dau gach ngang

Kb mình làm cho ( khá giài vì 2 câu mà )

= 270 nha bạn

1+1+2+2+3+3+4+4+5+5+6+6+7+7+8+8+9+9=2+4+6+8+10+12+14+16+18

                                                                        =(2+8)+(4+6)+10+(12+18)+(14+16)

                                                                        =10+10+10+30+30

                                                                        =30+30+30

                                                                        =30x3

                                                                        =90

= 270 nha

\(165-\left\{3\left[416-\left(5^2.3-71\right)^2\right]+10^2\right\}:20\)

\(=165-\left\{3\left[416-\left(25.3-71\right)^2\right]+100\right\}:20\)

\(=165-\left\{3\left[416-\left(4\right)^2\right]+100\right\}:20\)

 \(=165-\left\{3\left[416-16\right]+100\right\}:20\)

\(=165-\left\{3.400+100\right\}:2=165-1300:20\)

\(=165-65=100\)

minh dang can gap

=1 nhé

4 nhan 5 nhan 0,25nhan 1/5 nhan 1/2 nhan 2

=20x1/20x1

=1x1

=1 nè

Tui chơi bang bang trao đổi acc không

A.\(\frac{12}{15}>\frac{8}{15}\)

B.\(\frac{3}{8}< \frac{5}{6}\)

C.\(\frac{6}{7}< \frac{14}{3}\)

D.\(\frac{143}{144}>\frac{99}{100}\)

Nhớ k mình nha