1. Tìm y biết: 1 + 3 + 9 + 27 + … + y = 1093
Hãy nhập câu hỏi của bạn vào đây, nếu là tài khoản VIP, bạn sẽ được ưu tiên trả lời.
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
{ y + 1/3 } + { y + 1/9 } + { y + 1/27 } = 25/27
3y + 1/3 + 1/9 + 1/27= 25/27
3y+ 9/27+3/27+1/27= 25/27
3y + 13/27= 25/27
3y= 12/27
=> y= 4/27
![](https://rs.olm.vn/images/avt/0.png?1311)
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
\(\left(y+\frac{1}{3}\right) +\left(y+\frac{1}{9}\right)+ \left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)
\(y\cdot4+\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)=\frac{56}{81}\)
\(y\cdot4+\frac{40}{81}=\frac{56}{81}\)
\(y\cdot4=\frac{56}{81}-\frac{40}{81}\)
\(y\cdot4=\frac{16}{81}\)
\(y=\frac{16}{81}:4\)
\(y=\frac{4}{81}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\left(y+\frac{1}{3}\right)+\left(y+\frac{1}{9}\right)+\left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)
\(\Leftrightarrow4y+\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)=\frac{56}{81}\)
\(\Leftrightarrow4y+\frac{40}{81}=\frac{56}{81}\)
\(\Leftrightarrow4y=\frac{56}{81}-\frac{40}{81}\)
\(\Leftrightarrow4y=\frac{16}{81}\)
\(\Rightarrow y=\frac{16}{81}\div4\)
\(\Rightarrow y=\frac{4}{81}\)
Vậy y có giá trị =\(\frac{4}{81}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
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
![](https://rs.olm.vn/images/avt/0.png?1311)
![](https://rs.olm.vn/images/avt/0.png?1311)
-12/27 = 3x-1/9
=> -4/9 = 3x -1/9
=> 3x - 1 = -4
3x = -4 + 1 = -3
x = -3 : 3 = -1
3-x/45 = 2/9 = 1/2y
Ta có 3-x/45 = 2/9
=> 9(3-x) = 45 . 2
=> 9(3-x) = 90
3-x = 90 : 9 = 10
x = 3 - 10 = -7
2/9 = 1/2y
=> 2(2y) = 9 . 1
=> 4y = 9
y = 9 : 4 = 9/4
1+3+9+27+......+y=1093
3x(1+3+9+27+.....+y)=1093x3
3+9+27+81+.....+3y=1093x3
=> 1093x3-1093= (3+9+27+.....3y)-(1+3+9+27+....+y)
<=> 1093x2=3y-1
<=>2186+1=3y
<=> 2187=3y
=> y=2187:3
y=729