A=4+(2²+2³+2⁴+...+2²⁰)

                  A-4=2²+2³+2⁴+...+2²⁰

               2(A-4)=2³+2⁴+2⁵+...+2²¹

A-4=2(A-4)-(A-4)=(2³+2⁴+2⁵+...+2²¹)-(2²+2³+2⁴+...+2²⁰)

                   A-4=(2³-2³)+(2⁴-2⁴)+(2⁵-2⁵)+...+(2²⁰-2²⁰)+(2²¹-2²)

                   A-4=2²¹-4

                   A   =2²¹-4+4

                   A   =2²¹

Bạn làm tiếp nha . 

Giải hết hộ mik đi mà xin bạn

\(3^x+3^{x+2}+3^{x+3}=999\)

\(\Rightarrow3^x+3^x.3^2+3^x.3^3=999\)

\(\Rightarrow3^x.\left(1+3^2+3^3\right)=999\)

\(\Rightarrow3^x.37=999\)

\(\Rightarrow3^x=999:37\)

\(\Rightarrow3^x=27\)

\(\Rightarrow3^x=3^3\)

\(\Rightarrow x=3\)

\(3^x+3^{x+2}+3^{x+3}=999.\)

\(\Rightarrow3^x.\left(1+3^2+3^3\right)=999\)

\(\Rightarrow3^x.37=999\)

\(\Rightarrow3^x=999:37\)

\(\Rightarrow3^x=27\)

\(\Rightarrow3^x=3^3\)

\(\Rightarrow x=3\)

ứaedrfgthyjk

a) 2840 + [(999 - 9x) : 60 ] .24 = 3200

=> [(999-9x) : 60 ] . 24 = 2840 - 3200 = -360

=>  (999 - 9x) = \(\frac{-360}{24}=-15\)

=>  9x = 999 - ( - 15) = 999 + 15 = 1014

=>  x = \(\frac{1014}{9}=\frac{338}{3}\)

b) (3x - 48) . 6 = 3³.2² - 2³.3²

(3x - 48) . 6 = 27 . 4  -  8 . 9

(3x -48).6 = 36

(3x - 48 = 36 : 6 = 6

3x = 54

x = 54 : 3 =18

 t ick cho mik nha

120+[(999-9x):60].24=480 

[(999-9x):60].24 = 480 - 120 

[(999-9x):60].24 = 360

[(999-9x):60] = 360 : 24 

[(999-9x):60] = 15

(999-9x) = 15 x 60

(999-9x) = 900

9x = 999 - 900

9x = 99 

x = 99 : 9 

x = 11

120+[(999-9x):60]=480-120

[(999-9x):60].24=360

(999-9x):60=360:24

(999-9x):60=15

(999-9x)=15.60

999-9x=900

990x=900

x=990:900

x=?

\(\frac{25-x}{995}+\frac{21-x}{997}+\frac{17-x}{999}=\frac{11-x}{334}\)

\(\Rightarrow\frac{25-x}{995}+2+\frac{21-x}{997}+\frac{17-x}{999}+2=\frac{11-x}{334}+6\)

\(\Rightarrow\frac{25-x}{995}+\frac{1990}{995}+\frac{21-x}{997}+\frac{1994}{997}+\frac{17-x}{999}+\frac{1998}{999}=\frac{11-x}{334}+\frac{2004}{334}\)

\(\Rightarrow\frac{2015-x}{995}+\frac{2015-x}{997}+\frac{2015-x}{999}=\frac{2015-x}{334}\)

\(\Rightarrow\frac{2015-x}{995}+\frac{2015-x}{997}+\frac{2015-x}{999}-\frac{2015-x}{334}=0\)

\(\Rightarrow\left(2015-x\right)\left(\frac{1}{995}+\frac{1}{997}+\frac{1}{999}+\frac{1}{334}\right)=0\)

\(\Rightarrow2015-x=0\left(\text{vì }\frac{1}{995}+\frac{1}{997}+\frac{1}{999}+\frac{1}{334}\ne0\right)\)

\(\Rightarrow x=2015\)