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NT
1
7 tháng 5 2021
S= 23/2.5+23/5.8+....................+23/53.56
S=8/2.5+8/5.8+8/8.11+.......+8/53.56
S=8/3.(3/2.5+3/5.8+3/8.11+...........+3/53.56)
S=8/3.(1/2-1/5+1/5-1/8+1/8-...........+1/53-1/56)
S=8/3.(1/2-1/56)
S=8/3.27/56
S=9/7
nhớ t ick cho mình nha
H
4
19 tháng 2 2016
C=1-2+22-23+....+2100
D=1/5-1/52+1/53+.....+1/5101
E=4/2.5+4/5.8+..........+4/302.305
19 tháng 2 2016
C=1-2+22-23+....+2100
D=1/5-1/52+1/53+.....+1/5101
E=4/2.5+4/5.8+..........+4/302.305
9 tháng 3 2018
a. \(A=\dfrac{3}{2.5}+\dfrac{3}{5.8}+......+\dfrac{3}{17.20}\)
\(=\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+......+\dfrac{1}{17}-\dfrac{1}{20}\)
\(=\dfrac{1}{2}-\dfrac{1}{20}\)
\(=\dfrac{9}{20}\)
b. \(B=\dfrac{1}{20}+\dfrac{1}{30}+\dfrac{1}{42}+\dfrac{1}{56}+\dfrac{1}{72}+\dfrac{1}{90}\)
\(=\dfrac{1}{4.5}+\dfrac{1}{5.6}+\dfrac{1}{6.7}+\dfrac{1}{7.8}+\dfrac{1}{8.9}+\dfrac{1}{9.10}\)
\(=\dfrac{1}{4}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{6}+\dfrac{1}{6}-\dfrac{1}{7}+\dfrac{1}{7}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{9}+\dfrac{1}{9}-\dfrac{1}{10}\)
\(=\dfrac{1}{4}-\dfrac{1}{10}\)
\(=\dfrac{3}{20}\)
c. \(C=\dfrac{4^2}{1.5}+\dfrac{4^2}{5.9}+......+\dfrac{4^2}{45.49}\)
\(=4\left(\dfrac{4}{1.5}+\dfrac{4}{5.9}+....+\dfrac{4}{45.49}\right)\)
\(=4\left(1-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{9}+.....+\dfrac{1}{45}-\dfrac{1}{49}\right)\)
\(=4\left(1-\dfrac{1}{49}\right)\)
\(=4.\dfrac{48}{49}\)
\(=\dfrac{192}{49}\)
I
4
30 tháng 8 2017
a, dễ, tự làm
b, \(\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+.........+\dfrac{3x}{11.14}=\dfrac{1}{21}\)
\(\Leftrightarrow x\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+.........+\dfrac{3}{11.14}\right)=\dfrac{1}{21}\)
\(\Leftrightarrow x\left(\dfrac{1}{2}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+.....+\dfrac{1}{11}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
\(\Leftrightarrow x\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
\(\Leftrightarrow x.\dfrac{3}{7}=\dfrac{1}{21}\)
\(\Leftrightarrow x=\dfrac{1}{9}\)
Vậy ...
30 tháng 8 2017
a) (x-2)3 = (x-2)2
<=> (x-2)3-(x-2)2 = 0
<=> (x-2)2(x-2-1) = 0
<=> \(\left\{{}\begin{matrix}\left(x-2\right)^2=0\\x-3=0\end{matrix}\right.\)
<=> \(\left\{{}\begin{matrix}x=2\\x=3\end{matrix}\right.\)
b) \(\dfrac{3x}{2.5}+\dfrac{3x}{5.8}+...+\dfrac{3x}{11.14}=\dfrac{1}{21}\)
<=> \(x\left(\dfrac{3}{2.5}+\dfrac{3}{5.8}+...+\dfrac{3}{11.14}\right)=\dfrac{1}{21}\)
<=> \(x\left(\dfrac{1}{2}-\dfrac{1}{14}\right)=\dfrac{1}{21}\)
<=> \(x=\dfrac{1}{21}:\dfrac{3}{7}\)
<=> \(x=\dfrac{1}{9}\)
20 tháng 6 2017
Ta có : (6 - x)2014 = (6 - x)2015
=> (6 - x)2014 - (6 - x)2015 = 0
<=> (6 - x)2014(1 - 6 - x) = 0
<=> \(\orbr{\begin{cases}\left(6-x\right)^{2014}=0\\1-6-x=0\end{cases}}\)
<=> \(\orbr{\begin{cases}6-x=0\\-5-x=0\end{cases}}\)
<=> \(\orbr{\begin{cases}x=6\\x=-5\end{cases}}\)
20 tháng 6 2017
sory bạn trừng hợp hai mk nhầm :
1 - (6 - x) = 0
=> 1 - 6 + x = 0
=> -5 + x = 0
=> x = 5
21 tháng 3 2019
\(\frac{3^2}{8\cdot11}+\frac{3^2}{11\cdot14}+\frac{3^2}{14\cdot17}+...+\frac{3^2}{197\cdot200}\)
\(=3(\frac{1}{8}-\frac{1}{11}+...+\frac{1}{197}-\frac{1}{200})\)
\(=3(\frac{1}{8}-\frac{1}{200})\)
\(=3\cdot\frac{3}{25}=\frac{9}{25}\)
LG
21 tháng 3 2019
=3(1\(= 3(3/8.11+3/11.14+...+3/197.200) = 3(1/8-1/11+1/11-1/14+...+1/197-1/200) =3(1/8-1/200) =3/8-3/200 đề bạn ghi có chỗ nhầm nha \)
\(M= \dfrac{3^2}{2.5} +\dfrac{3^2}{5.8} +\dfrac{3^2}{8.11}+...+\dfrac{3^2}{98.101}\)
\(M= \) \( \dfrac{9}{2.5} +\dfrac{9}{5.8} +\dfrac{9}{8.11}+...+\dfrac{9}{98.101}\)
\(M=3(\dfrac{3}{2.5}+\dfrac{3}{5.8}+\dfrac{3}{8.11}+...+ \dfrac{3}{98.101})\)
\(M= 3(\dfrac{1}{2} -\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{8}+\dfrac{1}{8}-\dfrac{1}{11})\)
\(M= 3(\dfrac{1}{2}-\dfrac{1}{11})\)
\(M=3(\dfrac{11}{22}- \dfrac{2}{22})\)
\(M=3.\dfrac{9}{22}\)
\(M=\dfrac{27}{22}\)