Giải :

0,8 x 120 + 4 x 2 x 6 +8 x 2 +8 x 80

= 8 x 12 + 8 x 6 + 8 x 2 + 8 x 80

= 8 x ( 12 + 6 + 2 + 80 ) 

= 8 x 100

= 800

= 800 nha bạn

hok tốt

bạn nào trên 10 sp hoặc 10 sp k giúp mình ạ

sp á

là ...

điểm hỏi đáp k đúng đi

\(3x-1920=2x+120\Leftrightarrow x=2040\)

a) x . 3/5 = 2/3

<=> x     = 2/3 : 3/5

<=> x     = 2/3 . 5/3 

<=> x     = 10/9

Học tốt nha! :) 

TL

a)    5x + 20 = 110      

<=> x = 90 : 5 = 18

 b) x + 18 = - 13 

 <=> x = - 31

  c) 120 - x =  50   

   <=> x = 70     

 d) 10 - x = -29  

     <=>  x = 39

e) - x + 31 = 61

<=> x = -30

f) -85 - x = --70

<=> x = 15

Khi nào rảnh vào kênh H-EDITOR xem vid nha!!! Thanks!

gõ latex đi bn!

a. 2^x + 70 = 74

<=> 2^x = 4

<=> x = 2

b. 120 - \(\dfrac{4x}{2}\) = 80

<=> 120 - 2x = 80

<=> 120 - 80 = 2x

<=> 2x = 40

<=> x = 20

c. (3x + 5)² = 400

<=> \(|3x+5|=\sqrt{400}\)

<=> \(|3x+5|=20\)

<=> \(\left[{}\begin{matrix}3x+5=20\\3x+5=-20\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=5\\x=\dfrac{-25}{3}\end{matrix}\right.\) 

\(\dfrac{5x}{4}=\dfrac{80}{120}\\ =>\dfrac{5x}{4}=\dfrac{2}{3}\\ =>5x.3=2.4\\ 5x.3=8\\ 5x=\dfrac{8}{3}\\ x=\dfrac{8}{3}:5\\ x=\dfrac{8}{15}\)

\(\dfrac{5x}{4}=\dfrac{80}{120}\)

\(\Rightarrow5x=\dfrac{4.120}{80}\)

\(\Rightarrow5x=6\)

\(\Rightarrow x=\dfrac{6}{5}\)

\(\frac{1}{4}+\frac{1}{8}+\frac{1}{24}+\frac{1}{48}+\frac{1}{80}+\frac{1}{120}+\frac{1}{168}\)

\(=\frac{1}{4}.\left(1+\frac{1}{2}+\frac{1}{6}+\frac{1}{12}+\frac{1}{20}+\frac{1}{30}+\frac{1}{42}\right)\)

\(=\frac{1}{4}.\left(1+\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+\frac{1}{4.5}+\frac{1}{5.6}+\frac{1}{6.7}\right)\)

\(=\frac{1}{4}.\left(1+1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+\frac{1}{4}-\frac{1}{5}+\frac{1}{5}-\frac{1}{6}+\frac{1}{6}-\frac{1}{7}\right)\)

\(=\frac{1}{4}.\left(1+1-\frac{1}{7}\right)\)

\(=\frac{1}{4}.\left(2-\frac{1}{7}\right)\)

\(=\frac{1}{4}.\frac{13}{7}=\frac{13}{28}\)

Là 1 phần 4 + 1phan 8+ va cu nhu the

                Ta có : 

           Đặt    \(A=\frac{1}{8}+\frac{1}{24}+\frac{1}{48}+\frac{1}{80}+\frac{1}{120}+\frac{1}{168}\)

                   \(A=\frac{1}{2.4}+\frac{1}{4.6}+\frac{1}{6.8}+\frac{1}{8.10}+\frac{1}{10.12}+\frac{1}{12.14}\)

                 \(2A=\frac{2}{2.4}+\frac{2}{4.6}+\frac{2}{6.8}+\frac{2}{8.10}+\frac{2}{10.12}+\frac{2}{12.14}\)

                \(2A=\frac{1}{2}-\frac{1}{4}+\frac{1}{4}-\frac{1}{6}+\frac{1}{6}-\frac{1}{8}+\frac{1}{8}-\frac{1}{10}+\frac{1}{10}-\frac{1}{12}+\frac{1}{12}-\frac{1}{14}\)

                \(2A=\frac{1}{2}-\frac{1}{14}\)

                \(2A=\frac{7}{14}-\frac{1}{14}=\frac{3}{7}\)

                  \(A=\frac{3}{7}:2=\frac{3}{14}\)

           => \(\frac{1}{4}+\frac{3}{14}=\frac{7}{28}+\frac{6}{28}=\frac{13}{28}\)

           Ủng hộ mk nha !!! ^_^