4 x y + (1/3 + 1/9 + 1/27 + 1/81) = 56/81

4 x y + (27/81 + 9/81 + 3/81 + 1/81) = 56/81

4 x y + 40/81 = 56/81

4 x y  = 56/81 - 40/81 = 16/81

y = 4/81

\(\left(y+\frac{1}{3}\right) +\left(y+\frac{1}{9}\right)+ \left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)

\(y\cdot4+\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)=\frac{56}{81}\)

\(y\cdot4+\frac{40}{81}=\frac{56}{81}\)

\(y\cdot4=\frac{56}{81}-\frac{40}{81}\)

\(y\cdot4=\frac{16}{81}\)

     \(y=\frac{16}{81}:4\)

      \(y=\frac{4}{81}\)

(y+1/3)+(y+1/9)+(y+1/27)+(y+1/81)=56/81

=> y+1/3+y+1/9+y+1/27+y+1/81=56/81

=>4y+ 27/81+9/81+3/81+1/81=56/81

=> 4y+40/81=56/81

=>4y=16/81

=>y=4/81

a) (x+1)/3 + (x+1)/9 + (x+1)/27 + (x+1)/81 = 56/81 
<=> (27x+27)/81 + (9x+9)/81 + (3x+3)/81 + (x+1)/81 = 56/81 (quy đồng) 
<=> 27x + 9x + 3x + x + 27 + 9 + 3 + 1 = 56 (khử mẫu) 
<=> 40x = 56- 40 = 16 
<=> x = 16/40 = 2/5 

~ hok tốt ~

Đ/s:\(\frac{2}{5}\)

~Hok tốt~

#)Giải :

 \(\left(y+\frac{1}{3}\right)+\left(y+\frac{1}{9}\right)+\left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)

                                        \(4y+\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)=\frac{56}{81}\)

                                     \(4y+\left(\frac{27}{81}+\frac{9}{81}+\frac{3}{81}+\frac{1}{81}\right)=\frac{56}{81}\)

                                                                               \(4y+\frac{40}{81}=\frac{56}{81}\)

                                                                                      \(\Leftrightarrow4y=\frac{16}{81}\)

                                                                                         \(\Leftrightarrow y=\frac{4}{81}\)

y + 1/3 + y+ 1/9 +y +1/27 + y+ 1/81 =56/81

4y +(1/3 +1/9+1/27+1/81) = 56/81

4y +(27 +9+3+1/81)=56/81

4y +40/81=56/81

4y =56/81 -40/81

4y=16/81

y=16/81 .1/4

y=4/81

( y + 1/3 ) + ( y + 1/9 ) + ( y + 1/27 ) + ( y + 1/81 ) = 56/81

4y + (1/3 + 1/9 + 1/27 + 1/81) = 56/81

4y + (27/81 + 9/81 + 3/81 + 1/81) = 56/81

4y + 40/81 = 56/81

4y = 56/81 - 40/81

4y = 16/81

x= 16/81 : 4

x= 4/81 

Câu trả lời hay nhất:   ( y + 1/3 ) + ( y + 1/9 ) + (y + 1/27 ) + ( y + 1/81 ) = 56/81 
<=> (3y+1)/3 + (9y+1)/9 + (27y+1)/27 + (81y+1)/81 = 56/81 (quy đồng mẫu số trong các dấu ngoặc) 
<=> (81y+27)/81 + (81y+9)/81 + (81y+3)/81 + (81y+1)/81 = 56/81 (quy đồng mẫu số vế trái) 
<=> 4.81y + 27 + 9 + 3 + 1 = 56 (khử mẫu 81 + đặt nhân tử chung là 81y để đc 4 lần 81y tính sẽ nhanh) 
<=> 324y + 40 = 56 
<=> y = (56 - 40)/324 = 4/81 

\(\left(y+\frac{1}{3}\right)+\left(y+\frac{1}{9}\right)+\left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)

\(\Leftrightarrow4y+\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)=\frac{56}{81}\)

\(\Leftrightarrow4y+\frac{40}{81}=\frac{56}{81}\)

\(\Leftrightarrow4y=\frac{56}{81}-\frac{40}{81}\)

\(\Leftrightarrow4y=\frac{16}{81}\)

\(\Rightarrow y=\frac{16}{81}\div4\)

\(\Rightarrow y=\frac{4}{81}\)

Vậy y có giá trị =\(\frac{4}{81}\)

< y   1/3 >    < y   1/9>  < y   1/27 >   < y   1/81 > =  56 / 81   

= 4y + < 1/3 + 1/9 + 1/27 + 1/81 >  = 56 / 81

= 4y + 40 / 81 = 56 / 81 

= 4y = 56 / 81 - 40 / 81

= 4 / 81

Tìm y :

( y + 1/3 ) + ( y + 1/9 ) + ( y + 1/27 ) + ( y + 1/81 ) = 56/81

 y + 1/3 + y + 1/9 + y + 1/27 + y  + 1/81 = 56/81

 y x 4 + ( 1/3 + 1/9 + 1/27 +1/81 ) = 56/81

 y x 4 + ( 27/81 + 9/81 + 3/81 + 1/81 ) = 56/81

 y x 4 + 40/81 = 56/81

 y x 4              = 56/81 - 40/81

 y x 4              = 16/81

 y                    = 16/81 : 4

 y                    = 4/81

thanks Vũ Thị Huyền nha

Bài 1:
$(y+\frac{1}{3})+(y+\frac{1}{9})+(y+\frac{1}{27})+(y+\frac{1}{81})=\frac{56}{81}$

$(y+y+y+y)+(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81})=\frac{56}{81}$
$4\times y+\frac{40}{81}=\frac{56}{81}$

$4\times y=\frac{56}{81}-\frac{40}{81}=\frac{16}{81}$
$y=\frac{16}{81}:4=\frac{4}{81}$

Bài 2:

$18: \frac{x\times 0,4+0,32}{x}+5=14$

$18: \frac{x\times 0,4+0,32}{x}=14-5=9$

$\frac{x\times 0,4+0,32}{x}=18:9=2$

$x\times 0,4+0,32=2\times x$

$2\times x-x\times 0,4=0,32$

$x\times (2-0,4)=0,32$
$x\times 1,6=0,32$
$x=0,32:1,6=0,2$

Bài 3:

$\frac{3\times x}{2}=\frac{2}{5}+x+\frac{1}{3}$

$1,5\times x=x+\frac{11}{15}$

$1,5\times x-x=\frac{11}{15}$

$x\times (1,5-1)=\frac{11}{15}$

$x\times 0,5=\frac{11}{15}$

$x=\frac{11}{15}: 0,5=\frac{22}{15}$

1, \(\frac{1}{2}-\left(6\frac{5}{9}+x-\frac{117}{8}\right):\left(12\frac{1}{9}\right)=0\)

   \(\left(\frac{6.9+5}{9}+x-\frac{117}{8}\right):\frac{12.9+1}{9}=\frac{1}{2}\)

 ( . là nhân nha) 

    \(\left(\frac{59}{9}-\frac{117}{8}+x\right):\frac{109}{9}=\frac{1}{2}\)

    \(\frac{59}{9}-\frac{117}{8}+x=\frac{1}{2}\cdot\frac{109}{9}\)

    \(\frac{59}{9}-\frac{117}{8}+x=\frac{109}{18}\)

   \(x=\frac{109}{18}-\frac{59}{9}+\frac{117}{8}\)

\(x=\frac{113}{8}\)

( \(\left(y+\frac{1}{3}\right)+\left(y+\frac{2}{9}\right)+\left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)

   \(y+\frac{1}{3}+y+\frac{2}{9}+y+\frac{1}{27}+y+\frac{1}{81}=\frac{56}{81}\)

\(4y+\frac{1}{3}+\frac{2}{9}+\frac{1}{27}+\frac{1}{81}=\frac{56}{81}\)

\(4y+\frac{49}{81}=\frac{56}{81}\)

\(4y=\frac{7}{81}\)

y      =  7/81:4

y       = 7/324

1)

dãy trên có số chữ số là:

( 26 - 4 ) : 2 + 1 = 12 chữ số

tổng là:

( 26 + 4 ) x 12 : 2 = 180

ta có:

x + 180 = 210

x          = 210 - 180

x          = 30