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a1+1/3+1/9+1/27+1/81=?
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NT
Nguyễn Thị Thương Hoài
Giáo viên
VIP
25 tháng 7 2023
(y + \(\dfrac{1}{3}\)) + ( y + \(\dfrac{1}{9}\)) + ( y + \(\dfrac{1}{27}\)) + ( y + \(\dfrac{1}{81}\)) = \(\dfrac{56}{81}\)
( y + y + y + y ) + (\(\dfrac{1}{3}\)+ \(\dfrac{1}{9}\) + \(\dfrac{1}{27}\) + \(\dfrac{1}{81}\)) = \(\dfrac{56}{81}\)
4\(y\) + ( \(\dfrac{27}{81}\) + \(\dfrac{9}{81}\) + \(\dfrac{3}{27}\) + \(\dfrac{1}{81}\) ) = \(\dfrac{56}{81}\)
4y + \(\dfrac{40}{81}\) = \(\dfrac{56}{81}\)
4y = \(\dfrac{56}{81}\) - \(\dfrac{40}{81}\)
4y = \(\dfrac{16}{81}\)
y = \(\dfrac{16}{81}\) : 4
y = \(\dfrac{4}{81}\)
H9
HT.Phong (9A5)
CTVHS
25 tháng 7 2023
\(\left(y+\dfrac{1}{3}\right)+\left(y+\dfrac{1}{9}\right)+\left(y+\dfrac{1}{27}\right)+\left(y+\dfrac{1}{81}\right)=\dfrac{56}{81}\)
\(\Rightarrow y+\dfrac{1}{3}+y+\dfrac{1}{9}+y+\dfrac{1}{27}+y+\dfrac{1}{81}=\dfrac{56}{81}\)
\(\Rightarrow4\times y+\dfrac{40}{81}=\dfrac{56}{81}\)
\(\Rightarrow4\times y=\dfrac{56}{81}-\dfrac{40}{81}\)
\(\Rightarrow4\times y=\dfrac{16}{81}\)
\(\Rightarrow y=\dfrac{16}{81}:4\)
\(\Rightarrow y=\dfrac{4}{81}\)
TT
5
5 tháng 6 2019
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 ~
NN
Nguyễn Ngọc Anh Minh
CTVHS
VIP
29 tháng 11 2023
\(3S=241+81+27+9+...+\dfrac{1}{9}+\dfrac{1}{27}\)
\(2S=3S-S=241-\dfrac{1}{81}=\dfrac{241x81-1}{81}\)
\(\Rightarrow S=\dfrac{241x81-1}{2x81}\)
VT
9
4 tháng 8 2016
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
4 tháng 8 2016
\(\left(y+\frac{1}{3}\right) +\left(y+\frac{1}{9}\right)+ \left(y+\frac{1}{27}\right)+\left(y+\frac{1}{81}\right)=\frac{56}{81}\)
\(y\cdot4+\left(\frac{1}{3}+\frac{1}{9}+\frac{1}{27}+\frac{1}{81}\right)=\frac{56}{81}\)
\(y\cdot4+\frac{40}{81}=\frac{56}{81}\)
\(y\cdot4=\frac{56}{81}-\frac{40}{81}\)
\(y\cdot4=\frac{16}{81}\)
\(y=\frac{16}{81}:4\)
\(y=\frac{4}{81}\)
LA
20 tháng 6 2018
-1+1/3-1/9+1/27-1/81
=-81/81+27/81-9/81-3/81-1/81
=-67/81
đáp án đúng đó nha
20 tháng 6 2018
\(-1+\frac{1}{3}-\frac{1}{9}+\frac{1}{27}-\frac{1}{81}\)
\(=-1+(\frac{1}{3}-\frac{1}{3^2})+(\frac{1}{3^3}-\frac{1}{3^4})\)
\(=-1+\frac{3-1}{3^2}+\frac{3-1}{3^4}\)
\(=-1+\frac{2}{3^2}+\frac{2}{3^4}\)
\(=-1+(\frac{2}{9}+\frac{2}{81})\)
\(=-1+\frac{20}{81}\)
\(=\frac{-61}{81}\)
NM
16 tháng 8 2023
\(G=\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{81}+\dfrac{1}{243}\\ G=\dfrac{81}{243}+\dfrac{27}{243}+\dfrac{9}{243}+\dfrac{3}{243}+\dfrac{1}{243}\\ G=\dfrac{121}{243}\)
YN
31 tháng 1 2023
Đặt \(V=\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{81}+...+\dfrac{1}{729}+\dfrac{1}{2187}\)
\(\Rightarrow3V=3.\left(\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{81}+...+\dfrac{1}{729}+\dfrac{1}{2187}\right)\)
\(\Rightarrow3V=1+\left(\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\dfrac{1}{81}+...+\dfrac{1}{729}\right)\)
\(\Rightarrow3V=1+V-\dfrac{1}{2187}\)
\(\Rightarrow2V=1-\dfrac{1}{2187}\)
\(\Rightarrow V=\dfrac{1093}{2187}\).
1 tháng 2 2023
A = 1/3 + 1/9 + 1/27 + 1/81 +...+1/729 + 1/2187
3A = 1 + 1/3 + 1/9 + 1/27 + 1/81 +...+1/729
=>2A = 1 - 1/2187
=> A = ....
a, 1+1/3+1/9+1/27+1/81
=81/81+27/81+9/81+3/81+1/81
=81+27+9+3+1/81
=121/81